diff --git a/assembler/src/context.rs b/assembler/src/context.rs
new file mode 100644
index 0000000..dce4911
--- /dev/null
+++ b/assembler/src/context.rs
@@ -0,0 +1,21 @@
+//! This module contains the global asembler context to be passed to functions that need
+//! it.
+
+use std::sync::RwLock;
+
+use crate::{model::module_registry::ModuleRegistry, symtab::SymbolTable};
+
+/// Global state to be passed around.
+pub struct AssemblerContext {
+    pub symbol_table: RwLock<SymbolTable>,
+    pub module_registry: RwLock<ModuleRegistry>,
+}
+
+impl AssemblerContext {
+    pub fn new() -> Self {
+        Self {
+            symbol_table: RwLock::new(SymbolTable::new()),
+            module_registry: RwLock::new(ModuleRegistry::new()),
+        }
+    }
+}
diff --git a/assembler/src/error.rs b/assembler/src/error.rs
index a856590..483b68d 100644
--- a/assembler/src/error.rs
+++ b/assembler/src/error.rs
@@ -3,7 +3,7 @@
 
 use std::fmt::{Debug, Display};
 
-use crate::source::source_info::SourceInfo;
+use crate::source::{source_info::SourceInfo, tokeniser::error::TokeniserError};
 
 /// An error that may occur during the assembly of a set of source files.
 #[derive(Debug)]
@@ -13,26 +13,38 @@ pub struct AssembleError {
     source_info: Option<SourceInfo>,
     /// The type of assembly error that occurred.
     kind: AssembleErrorKind,
-    /// The formatter to handle printing the error.
-    formatter: Box<dyn ErrorFormatter>,
 }
 
 impl AssembleError {
-    pub fn new_source_error(source_info: SourceInfo, kind: AssembleErrorKind) -> Self {
+    #[must_use]
+    pub const fn new_source_error(
+        source_info: SourceInfo,
+        kind: AssembleErrorKind,
+    ) -> Self {
         Self {
             source_info: Some(source_info),
             kind,
-            formatter,
         }
     }
 
-    pub fn new_other_error(kind: AssembleErrorKind) {}
+    #[must_use]
+    pub const fn new_other_error(kind: AssembleErrorKind) -> Self {
+        Self {
+            source_info: None,
+            kind,
+        }
+    }
 }
 
 impl Display for AssembleError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.formatter
-            .write(f, self.source_info.as_ref(), &self.kind)
+        if let Some(info) = &self.source_info {
+            write!(f, "at {info}")?;
+        }
+
+        write!(f, "{}", self.kind)?;
+
+        Ok(())
     }
 }
 
@@ -42,7 +54,29 @@ impl std::error::Error for AssembleError {}
 /// Different types of errors that may occur when assembling a set of input source files.
 #[non_exhaustive]
 #[derive(Debug)]
-pub enum AssembleErrorKind {}
+pub enum AssembleErrorKind {
+    /// Usually unexpected I/O errors. Not normally recoverable.
+    IO(std::io::Error),
+    /// Errors emitted from the [`Tokeniser`].
+    Tokenise(TokeniserError),
+}
+
+impl Display for AssembleErrorKind {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Tokenise(why) => write!(f, "tokeniser error: {why}"),
+            _ => write!(
+                f,
+                "unhandled error type in Display implementation! See error.rs!"
+            ),
+        }
+    }
+}
+
+impl From<std::io::Error> for AssembleErrorKind {
+    fn from(err: std::io::Error) -> Self {
+        Self::IO(err)
+    }
+}
 
 pub mod conversions;
-pub mod formatters;
diff --git a/assembler/src/error/conversions.rs b/assembler/src/error/conversions.rs
index 2a89c19..8bb4731 100644
--- a/assembler/src/error/conversions.rs
+++ b/assembler/src/error/conversions.rs
@@ -2,6 +2,6 @@ use crate::error::AssembleError;
 
 impl From<std::io::Error> for AssembleError {
     fn from(err: std::io::Error) -> Self {
-        
+        Self::new_other_error(err.into())
     }
 }
diff --git a/assembler/src/lib.rs b/assembler/src/lib.rs
index c9433f2..22be5b9 100644
--- a/assembler/src/lib.rs
+++ b/assembler/src/lib.rs
@@ -15,6 +15,7 @@
 pub mod args;
 pub mod image_builder;
 // pub mod tooling;
+pub mod context;
 pub mod error;
 pub mod model;
 pub mod source;
diff --git a/assembler/src/model.rs b/assembler/src/model.rs
index 8969da3..75e8bc0 100644
--- a/assembler/src/model.rs
+++ b/assembler/src/model.rs
@@ -1,3 +1,5 @@
 //! This module contains the underlying data models and enums used by the Assembler.
 
+pub mod module;
+pub mod module_registry;
 pub mod symbol;
diff --git a/assembler/src/model/module.rs b/assembler/src/model/module.rs
new file mode 100644
index 0000000..620d5ce
--- /dev/null
+++ b/assembler/src/model/module.rs
@@ -0,0 +1,69 @@
+//! This module contains the [`Module`] type and associated types. Each compilation unit
+//! (file) is represented by a module which is used to namespace "function" calls and
+//! accesses to global variables.
+//!
+//! They have unique identifiers in the form of UUIDs.
+
+use std::path::{Path, PathBuf};
+
+use uuid::Uuid;
+
+use crate::model::module_registry::ModuleRegistry;
+
+/// The ID for a module. A tuple struct for type safety.
+#[derive(Debug, Hash, PartialEq, Eq, Clone, Copy)]
+pub struct ModuleId(Uuid);
+
+impl ModuleId {
+    pub fn from_module(module: Module) -> Self {
+        module.id
+    }
+
+    /// Convenience method to get the [`Module`] from a [`ModuleId`].
+    pub fn to_module<'m>(&self, registry: &'m ModuleRegistry) -> Option<&'m Module> {
+        registry.get(self)
+    }
+
+    /// Convenience method to get the [`Module`] name from a [`ModuleId`].
+    pub fn to_module_name<'m>(self, registry: &'m ModuleRegistry) -> Option<&'m str> {
+        if let Some(module) = self.to_module(&registry) {
+            Some(module.name.as_str())
+        } else {
+            None
+        }
+    }
+}
+
+impl std::fmt::Display for ModuleId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+/// A single source file or compilation unit. Stores its own symbol table.
+#[derive(Debug)]
+pub struct Module {
+    /// The name of the module. This is typically the name of the file, less the `.dsa`
+    /// extension.
+    pub name: String,
+    /// The file path to the module. This is an absolute path.
+    pub path: PathBuf,
+    /// A unique ID for this module.
+    pub id: ModuleId,
+}
+
+impl std::hash::Hash for Module {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.id.0.hash(state);
+    }
+}
+
+impl Module {
+    pub fn new<P: AsRef<Path>>(name: String, path: P) -> Self {
+        Self {
+            name,
+            path: path.as_ref().to_path_buf(),
+            id: ModuleId(Uuid::new_v4()),
+        }
+    }
+}
diff --git a/assembler/src/model/module_registry.rs b/assembler/src/model/module_registry.rs
new file mode 100644
index 0000000..0cd4054
--- /dev/null
+++ b/assembler/src/model/module_registry.rs
@@ -0,0 +1,36 @@
+//! This module contains the code for the module registry. This is a singleton storing all
+//! the modules being assembled.
+
+use std::collections::HashMap;
+
+use super::module::{Module, ModuleId};
+
+/// Stores all the [`Module`]'s to be assembled.
+pub struct ModuleRegistry {
+    modules: HashMap<ModuleId, Module>,
+}
+
+impl ModuleRegistry {
+    pub fn new() -> Self {
+        Self {
+            modules: HashMap::new(),
+        }
+    }
+
+    /// Gets a [`Module`] by ID.
+    pub fn get(&self, module_id: &ModuleId) -> Option<&Module> {
+        self.modules.get(module_id)
+    }
+
+    /// Adds a [`Module`] and returns its [`ModuleId`].
+    pub fn add(&mut self, module: Module) -> ModuleId {
+        let id = module.id;
+        self.modules.insert(id, module);
+        id
+    }
+
+    /// Returns an iterator of modules.
+    pub fn modules(&self) -> impl Iterator<Item = &Module> {
+        self.modules.values()
+    }
+}
diff --git a/assembler/src/model/symbol.rs b/assembler/src/model/symbol.rs
index 24fffc7..ea9b5cb 100644
--- a/assembler/src/model/symbol.rs
+++ b/assembler/src/model/symbol.rs
@@ -1,17 +1,58 @@
 //! This module contains the definitions for a Symbol.
 
+use std::collections::HashSet;
+
 use uuid::Uuid;
 
+use crate::{model::module::ModuleId, symtab::SymbolTable};
+
+/// Tuple struct for type safety. Has methods for fetching symbols by ID.
+#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
+pub struct SymbolId(Uuid);
+
+impl From<Symbol> for SymbolId {
+    fn from(sym: Symbol) -> Self {
+        sym.id
+    }
+}
+
+impl SymbolId {
+    pub fn new() -> Self {
+        Self(Uuid::new_v4())
+    }
+
+    /// Convenience method to get the [`Module`] from a [`ModuleId`].
+    pub fn to_module<'s>(&self, registry: &'s SymbolTable) -> Option<&'s Symbol> {
+        registry.get(self)
+    }
+
+    /// Convenience method to get the [`Module`] name from a [`ModuleId`].
+    pub fn to_module_name<'m>(self, registry: &'m SymbolTable) -> Option<&'m str> {
+        if let Some(module) = self.to_module(&registry) {
+            Some(module.name.as_str())
+        } else {
+            None
+        }
+    }
+}
+
 /// A symbol is a named reference that may be resolved later to an address by a linker.
+#[derive(Debug)]
 pub struct Symbol {
     /// Stored cheaply instead of the name. Shall be stored in the symbol table under
     /// this key.
-    pub id: Uuid,
+    pub id: SymbolId,
+
+    /// The human-readable name for the symbol.
+    pub name: String,
+
     pub visibility: Visibility,
+
     pub symbol_type: SymbolType,
 
-    /// The id of the module the symbol is defined in.
-    module_id: Uuid,
+    /// The id of the module the symbol is defined in. This will be different for symbols
+    /// in different objects.
+    pub module_id: ModuleId,
 
     /// Whether or not the symbol requires relocating.
     pub needs_relocation: bool,
@@ -30,21 +71,68 @@ pub struct Symbol {
     /// ```
     ///
     /// Where `main` depends on `another_func`.
-    pub dependencies: Vec<Uuid>,
+    pub dependencies: HashSet<SymbolId>,
+
+    /// The address of the symbol.
+    pub address: Option<u32>,
+    /// The section the symbol is in.
+    /// TODO: Perhaps make this a proper type?
+    pub section: Option<String>,
+    pub size: Option<u32>,
 }
 
 impl Symbol {
     pub fn new(
-        id: Uuid,
+        name: String,
+        module_id: ModuleId,
         visibility: Visibility,
         symbol_type: SymbolType,
-        module_id: Uuid,
     ) -> Self {
         Self {
-            id,
+            id: SymbolId::new(),
+            name,
+            module_id,
+            address: None,
+            section: None,
+            size: None,
             visibility,
             symbol_type,
-            module_id,
+            needs_relocation: false,
+            dependencies: HashSet::new(),
+        }
+    }
+
+    /// Adds a dependency on another [`Symbol`].
+    pub fn add_dependency(&mut self, dep: SymbolId) {
+        if self.id == dep {
+            return;
+        }
+
+        // We can resolve a lot of addresses at assembly time, but not really foreign
+        // ones, since we aren't certain of their position.
+        //
+        /* TODO: Handle this for flat binary case i.e. no linker required. This may be
+         *       done using a similar method to before, such as just concatenating all
+         * of the files together and handling jumps and halts.
+         *
+         * > Ask Harry or read the initial code.
+         */
+        if self.dependencies.insert(dep) {
+            self.needs_relocation = true;
+        }
+    }
+
+    /// Returns whether a [`Symbol`] depends on `symbol_id`.
+    pub fn depends_on(&self, symbol_id: &SymbolId) -> bool {
+        self.dependencies.contains(symbol_id)
+    }
+
+    /// Removes a [`Symbol`] from the dependency set.
+    pub fn remove_dependency(&mut self, symbol_id: &SymbolId) {
+        self.dependencies.remove(symbol_id);
+
+        if self.dependencies.is_empty() {
+            self.needs_relocation = false;
         }
     }
 }
@@ -63,7 +151,8 @@ pub enum Visibility {
     Weak,
 }
 
+#[derive(Debug)]
 pub enum SymbolType {
-    Function,
-    Label,
+    LabelOrFunction,
+    Variable,
 }
diff --git a/assembler/src/source.rs b/assembler/src/source.rs
index 5190d73..1146508 100644
--- a/assembler/src/source.rs
+++ b/assembler/src/source.rs
@@ -14,7 +14,5 @@ pub mod tokeniser;
 pub fn load_source_bytes<P: AsRef<Path>>(p: P) -> Result<Vec<u8>, AssembleError> {
     let path = p.as_ref();
 
-    let bytes = std::fs::read(path)?;
-
-    Ok(vec![])
+    Ok(std::fs::read(path)?)
 }
diff --git a/assembler/src/source/source_info.rs b/assembler/src/source/source_info.rs
index 5347a29..ff43b4a 100644
--- a/assembler/src/source/source_info.rs
+++ b/assembler/src/source/source_info.rs
@@ -1,17 +1,25 @@
 //! This file contains information on where a [`Token`] or [`Node`] is within the source
-//! code for more informative errors. This will likely be attached to a [`Token`] which
-//! will in turn be attached to an AST [`Node`].
+//! code for more informative errors.
+//!
+//! This will likely be attached to a [`Token`] which will in turn be attached to an AST
+//! [`Node`].
 
-use uuid::Uuid;
+use std::fmt::Display;
+
+use crate::model::module::Module;
 
 ///  Information on where the token is within the source.
 #[derive(Debug)]
 pub struct SourceInfo {
     /// The line number within the source file underpinned by `module_id`.
     pub line_no: usize,
-    /// The ID of the module containing this token. This will be looked up in the global
-    /// hashmap of [`Module`]'s.
-    pub module_id: Uuid,
+    pub module: Module,
     /// The indexes where this token may be found (line-local).
     pub span: std::ops::Range<usize>,
 }
+
+impl Display for SourceInfo {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.module.name)
+    }
+}
diff --git a/assembler/src/source/token.rs b/assembler/src/source/token.rs
index 094b078..ba3c8d1 100644
--- a/assembler/src/source/token.rs
+++ b/assembler/src/source/token.rs
@@ -2,16 +2,105 @@
 //! easier to build from scratch and edit his code than it would be to try and wrangle it
 //! into shape.
 
+use crate::source::source_info::SourceInfo;
+
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum TokenType {
-    Symbol(Symbol),
-    Register(Register),
+    /// Symbol reference (e.g., `loop_start`, `my_data`).
+    Symbol(SymbolToken),
+    /// CPU register (e.g., `r1`, `r2`, `sp`).
+    Register(RegisterToken),
+    /// Immediate value (e.g., `42`, `0xFF`).
     Immediate(u32),
-    StringLit(String),
-    Opcode(Opcode),
+    /// String literal (e.g., `"hello world"`).
+    String(String),
+    /// Assembly instruction (e.g., `add`, `jmp`, `nop`).
+    Instruction(InstructionToken),
+    /// Label definition (e.g., `loop_start:`).
+    Label(LabelToken),
+    /// Assembler directive (e.g., `.global`, `.section`, `.dw`).
+    Directive(DirectiveToken),
+    /// End of line.
+    Newline,
+    /// End of file.
+    Eof,
 }
 
+#[derive(Debug)]
 pub struct Token {
+    /// The type of the token.
     token_type: TokenType,
+    /// Where in the source code is this [`Token`]?
     source_info: SourceInfo,
 }
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct SymbolToken {
+    pub name: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct LabelToken {
+    pub name: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct DirectiveToken {
+    pub directive: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct RegisterToken {
+    pub name: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct InstructionToken {
+    pub mnemonic: String,
+}
+
+impl Token {
+    #[must_use]
+    pub const fn new(token_type: TokenType, source_info: SourceInfo) -> Self {
+        Self {
+            token_type,
+            source_info,
+        }
+    }
+
+    #[must_use]
+    pub const fn symbol(name: String, source_info: SourceInfo) -> Self {
+        Self::new(TokenType::Symbol(SymbolToken { name }), source_info)
+    }
+
+    #[must_use]
+    pub const fn label(name: String, source_info: SourceInfo) -> Self {
+        Self::new(TokenType::Label(LabelToken { name }), source_info)
+    }
+
+    #[must_use]
+    pub const fn instruction(mnemonic: String, source_info: SourceInfo) -> Self {
+        Self::new(
+            TokenType::Instruction(InstructionToken { mnemonic }),
+            source_info,
+        )
+    }
+
+    #[must_use]
+    pub const fn register(name: String, source_info: SourceInfo) -> Self {
+        Self::new(TokenType::Register(RegisterToken { name }), source_info)
+    }
+
+    #[must_use]
+    pub const fn immediate(value: u32, source_info: SourceInfo) -> Self {
+        Self::new(TokenType::Immediate(value), source_info)
+    }
+
+    #[must_use]
+    pub const fn directive(directive: String, source_info: SourceInfo) -> Self {
+        Self::new(
+            TokenType::Directive(DirectiveToken { directive }),
+            source_info,
+        )
+    }
+}
diff --git a/assembler/src/source/tokeniser.rs b/assembler/src/source/tokeniser.rs
index 8bbe489..902fc68 100644
--- a/assembler/src/source/tokeniser.rs
+++ b/assembler/src/source/tokeniser.rs
@@ -3,3 +3,5 @@
 
 /// Consumes a [`Vec<u8>`] and outputs a [`Vec`] of [Token]'s.
 pub struct Tokeniser {}
+
+pub mod error;
diff --git a/assembler/src/source/tokeniser/error.rs b/assembler/src/source/tokeniser/error.rs
new file mode 100644
index 0000000..0af204a
--- /dev/null
+++ b/assembler/src/source/tokeniser/error.rs
@@ -0,0 +1,10 @@
+//! This module contains the error types for the tokeniser.
+
+#[derive(Debug)]
+pub enum TokeniserError {}
+
+impl std::fmt::Display for TokeniserError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "TODO!!!!!!")
+    }
+}
diff --git a/assembler/src/symtab.rs b/assembler/src/symtab.rs
index 45d913f..7fe473e 100644
--- a/assembler/src/symtab.rs
+++ b/assembler/src/symtab.rs
@@ -4,7 +4,118 @@
 //! It is also required for detection of duplicate symbols, and resolution in the flat
 //! binary output type.
 
-/// Stored for each compilation unit (called a [`Module`]).
-///
-/// One hashmap maps [`Symbol`] ID's to their corresponding structs, and 
-pub struct SymbolTable
+use crate::{
+    error::AssembleError,
+    model::{
+        module::ModuleId,
+        symbol::{Symbol, SymbolId, Visibility},
+    },
+};
+use std::collections::HashMap;
+
+/// Global symbol table - single source of truth for all symbols.
+/// Much simpler than per-module tables.
+#[derive(Debug)]
+pub struct SymbolTable {
+    /// All symbols by their ID - O(1) lookup
+    symbols: HashMap<SymbolId, Symbol>,
+    /// Name to ID mapping for human-readable lookups - O(1) lookup
+    name_to_id: HashMap<String, SymbolId>,
+    /// Module to symbols mapping for module-specific queries
+    module_symbols: HashMap<ModuleId, Vec<SymbolId>>,
+}
+
+impl SymbolTable {
+    #[must_use]
+    pub fn new() -> Self {
+        Self {
+            symbols: HashMap::new(),
+            name_to_id: HashMap::new(),
+            module_symbols: HashMap::new(),
+        }
+    }
+
+    /// Adds a symbol to the global table
+    pub fn add_symbol(&mut self, symbol: Symbol) -> Result<SymbolId, AssembleError> {
+        let id = symbol.id;
+        let module_id = symbol.module_id;
+        let name = symbol.name.clone();
+
+        // Check for duplicate names in the same module
+        if let Some(&existing_id) = self.name_to_id.get(&name)
+            && let Some(existing) = self.symbols.get(&existing_id)
+            && existing.module_id == module_id
+        {
+            return Err(AssembleError::new_other_error(
+                crate::error::AssembleErrorKind::IO(std::io::Error::new(
+                    std::io::ErrorKind::AlreadyExists,
+                    format!("Symbol '{name}' already defined in module"),
+                )),
+            ));
+        }
+
+        // Add to all mappings
+        self.name_to_id.insert(name, id);
+        self.symbols.insert(id, symbol);
+        self.module_symbols.entry(module_id).or_default().push(id);
+
+        Ok(id)
+    }
+
+    /// Gets the [`Symbol`] by its [`SymbolId`].
+    pub fn get(&self, id: &SymbolId) -> Option<&Symbol> {
+        self.symbols.get(id)
+    }
+
+    /// Gets the [`Symbol`] by its name.
+    pub fn get_by_name(&self, name: &str) -> Option<&Symbol> {
+        self.name_to_id
+            .get(name)
+            .and_then(|id| self.symbols.get(id))
+    }
+
+    /// Gets all [`Symbol`]s in a module.
+    pub fn get_module_symbols(&self, module_id: &ModuleId) -> Vec<&Symbol> {
+        self.module_symbols
+            .get(module_id)
+            .map(|ids| ids.iter().filter_map(|id| self.symbols.get(id)).collect())
+            .unwrap_or_default()
+    }
+
+    /// Gets all the public symbols.
+    pub fn get_public_symbols(&self) -> Vec<&Symbol> {
+        self.symbols
+            .values()
+            .filter(|sym| matches!(sym.visibility, Visibility::Public))
+            .collect()
+    }
+
+    /// Updates symbol address (during resolution). Used for flat binaries or symbols with
+    /// no relocations.
+    pub fn update_symbol_address(
+        &mut self,
+        id: &SymbolId,
+        address: u32,
+    ) -> Result<(), AssembleError> {
+        if let Some(symbol) = self.symbols.get_mut(id) {
+            symbol.address = Some(address);
+            if symbol.dependencies.is_empty() {
+                symbol.needs_relocation = false;
+            }
+            Ok(())
+        } else {
+            Err(AssembleError::new_other_error(
+                crate::error::AssembleErrorKind::IO(std::io::Error::new(
+                    std::io::ErrorKind::NotFound,
+                    "Symbol not found",
+                )),
+            ))
+        }
+    }
+}
+
+impl Default for SymbolTable {
+    fn default() -> Self {
+        Self::new()
+    }
+}