diff --git a/crates/oxide_compiler/src/compiler.rs b/crates/oxide_compiler/src/compiler.rs
new file mode 100644
index 0000000..8ea1bc2
--- /dev/null
+++ b/crates/oxide_compiler/src/compiler.rs
@@ -0,0 +1,308 @@
+use crate::module::CompiledModule;
+use crate::opcode::{self, OpCode};
+
+pub use oxide_parser::{BinaryOperator, Expression, Statement, UnaryOperator};
+
+/// Literal constant stored in bytecode module's constant pool.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Constant {
+    Number(f64),
+    String(String),
+    Boolean(bool),
+    Null,
+    Undefined,
+}
+
+pub struct Compiler;
+
+struct CompileCtx {
+    bytecode: Vec<opcode::Instr>,
+    constants: Vec<Constant>,
+    next_reg: u8,
+    max_regs: u8,
+}
+
+impl CompileCtx {
+    fn new() -> Self {
+        Self {
+            bytecode: Vec::new(),
+            constants: Vec::new(),
+            next_reg: 0,
+            max_regs: 0,
+        }
+    }
+
+    fn emit(&mut self, instr: opcode::Instr) {
+        self.bytecode.push(instr);
+    }
+
+    fn alloc_reg(&mut self) -> u8 {
+        let r = self.next_reg;
+        self.next_reg += 1;
+        if self.next_reg > self.max_regs {
+            self.max_regs = self.next_reg;
+        }
+        r
+    }
+
+    fn reset_regs(&mut self) {
+        self.next_reg = 0;
+    }
+
+    fn add_constant(&mut self, c: Constant) -> u16 {
+        if let Some(idx) = self.constants.iter().position(|x| x == &c) {
+            return idx as u16;
+        }
+        let idx = self.constants.len();
+        self.constants.push(c);
+        idx as u16
+    }
+}
+
+impl Compiler {
+    pub fn new() -> Self {
+        Self
+    }
+
+    pub fn compile(&self, program: &oxide_parser::Program) -> Result<CompiledModule, String> {
+        let mut ctx = CompileCtx::new();
+
+        for stmt in &program.body {
+            self.count_statement(stmt, &mut ctx);
+        }
+        ctx.max_regs = ctx.max_regs.max(1);
+        ctx.reset_regs();
+
+        for stmt in &program.body {
+            self.emit_statement(stmt, &mut ctx)?;
+        }
+        ctx.emit(opcode::encode(OpCode::HALT, 0, 0, 0));
+
+        Ok(CompiledModule {
+            bytecode: ctx.bytecode,
+            constants: ctx.constants,
+            n_registers: ctx.max_regs,
+        })
+    }
+}
+
+impl Default for Compiler {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+// ── Pass 1: Counter ──
+
+impl Compiler {
+    fn count_statement(&self, stmt: &Statement, ctx: &mut CompileCtx) {
+        match stmt {
+            Statement::ExpressionStatement(es) => {
+                self.count_expression(&es.expression, ctx);
+            }
+            Statement::VariableDeclaration(decl) => {
+                for d in &decl.declarations {
+                    if let Some(init) = &d.init {
+                        self.count_expression(init, ctx);
+                    }
+                }
+            }
+            Statement::ReturnStatement(ret) => {
+                if let Some(arg) = &ret.argument {
+                    self.count_expression(arg, ctx);
+                }
+            }
+            Statement::IfStatement(ifs) => {
+                self.count_expression(&ifs.test, ctx);
+                self.count_statement(&ifs.consequent, ctx);
+                if let Some(alt) = &ifs.alternate {
+                    self.count_statement(alt, ctx);
+                }
+            }
+            Statement::WhileStatement(wh) => {
+                self.count_expression(&wh.test, ctx);
+                self.count_statement(&wh.body, ctx);
+            }
+            Statement::ForStatement(fr) => {
+                if let Some(init) = &fr.init {
+                    if let Some(expr) = init.as_expression() {
+                        self.count_expression(expr, ctx);
+                    }
+                }
+                if let Some(test) = &fr.test {
+                    self.count_expression(test, ctx);
+                }
+                if let Some(update) = &fr.update {
+                    self.count_expression(update, ctx);
+                }
+                self.count_statement(&fr.body, ctx);
+            }
+            Statement::BlockStatement(block) => {
+                for s in &block.body {
+                    self.count_statement(s, ctx);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn count_expression(&self, expr: &Expression, ctx: &mut CompileCtx) {
+        match expr {
+            Expression::BinaryExpression(bin) => {
+                self.count_expression(&bin.left, ctx);
+                self.count_expression(&bin.right, ctx);
+                ctx.alloc_reg();
+            }
+            Expression::UnaryExpression(un) => {
+                self.count_expression(&un.argument, ctx);
+                ctx.alloc_reg();
+            }
+            Expression::CallExpression(call) => {
+                self.count_expression(&call.callee, ctx);
+                ctx.alloc_reg();
+            }
+            Expression::AssignmentExpression(assign) => {
+                self.count_expression(&assign.right, ctx);
+                ctx.alloc_reg();
+            }
+            Expression::ConditionalExpression(cond) => {
+                self.count_expression(&cond.test, ctx);
+                self.count_expression(&cond.consequent, ctx);
+                self.count_expression(&cond.alternate, ctx);
+                ctx.alloc_reg();
+            }
+            Expression::SequenceExpression(seq) => {
+                for e in &seq.expressions {
+                    self.count_expression(e, ctx);
+                }
+            }
+            Expression::LogicalExpression(log) => {
+                self.count_expression(&log.left, ctx);
+                self.count_expression(&log.right, ctx);
+                ctx.alloc_reg();
+            }
+            _ => {
+                ctx.alloc_reg();
+            }
+        }
+    }
+}
+
+// ── Pass 2: Emitter ──
+
+impl Compiler {
+    fn emit_statement(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<(), String> {
+        match stmt {
+            Statement::ExpressionStatement(es) => {
+                self.emit_expression(&es.expression, ctx)?;
+            }
+            Statement::VariableDeclaration(decl) => {
+                for d in &decl.declarations {
+                    if let Some(init) = &d.init {
+                        self.emit_expression(init, ctx)?;
+                    }
+                }
+            }
+            Statement::ReturnStatement(ret) => match &ret.argument {
+                Some(expr) => {
+                    let r = self.emit_expression(expr, ctx)?;
+                    ctx.emit(opcode::encode(OpCode::RETURN, r, 0, 0));
+                }
+                None => {
+                    ctx.emit(opcode::encode(OpCode::RETURN, 0, 0, 0));
+                }
+            },
+            Statement::BlockStatement(block) => {
+                for s in &block.body {
+                    self.emit_statement(s, ctx)?;
+                }
+            }
+            _ => {}
+        }
+        Ok(())
+    }
+
+    fn emit_expression(&self, expr: &Expression, ctx: &mut CompileCtx) -> Result<u8, String> {
+        match expr {
+            Expression::NumericLiteral(n) => {
+                let idx = ctx.add_constant(Constant::Number(n.value));
+                let r = ctx.alloc_reg();
+                ctx.emit(opcode::encode(
+                    OpCode::LOAD_CONST,
+                    r,
+                    (idx & 0xFF) as u8,
+                    ((idx >> 8) & 0xFF) as u8,
+                ));
+                Ok(r)
+            }
+            Expression::StringLiteral(s) => {
+                let idx = ctx.add_constant(Constant::String(s.value.to_string()));
+                let r = ctx.alloc_reg();
+                ctx.emit(opcode::encode(
+                    OpCode::LOAD_CONST,
+                    r,
+                    (idx & 0xFF) as u8,
+                    ((idx >> 8) & 0xFF) as u8,
+                ));
+                Ok(r)
+            }
+            Expression::BooleanLiteral(b) => {
+                let idx = ctx.add_constant(Constant::Boolean(b.value));
+                let r = ctx.alloc_reg();
+                ctx.emit(opcode::encode(
+                    OpCode::LOAD_CONST,
+                    r,
+                    (idx & 0xFF) as u8,
+                    ((idx >> 8) & 0xFF) as u8,
+                ));
+                Ok(r)
+            }
+            Expression::NullLiteral(_) => {
+                let idx = ctx.add_constant(Constant::Null);
+                let r = ctx.alloc_reg();
+                ctx.emit(opcode::encode(
+                    OpCode::LOAD_CONST,
+                    r,
+                    (idx & 0xFF) as u8,
+                    ((idx >> 8) & 0xFF) as u8,
+                ));
+                Ok(r)
+            }
+            Expression::BinaryExpression(bin) => {
+                let left = self.emit_expression(&bin.left, ctx)?;
+                let right = self.emit_expression(&bin.right, ctx)?;
+                let op = match bin.operator {
+                    BinaryOperator::Addition => OpCode::ADD,
+                    BinaryOperator::Subtraction => OpCode::SUB,
+                    BinaryOperator::Multiplication => OpCode::MUL,
+                    BinaryOperator::Division => OpCode::DIV,
+                    BinaryOperator::Remainder => OpCode::MOD,
+                    BinaryOperator::Equality => OpCode::EQ,
+                    BinaryOperator::Inequality => OpCode::NEQ,
+                    BinaryOperator::LessThan => OpCode::LT,
+                    BinaryOperator::GreaterThan => OpCode::GT,
+                    BinaryOperator::LessEqualThan => OpCode::LTE,
+                    BinaryOperator::GreaterEqualThan => OpCode::GTE,
+                    _ => return Err(format!("unsupported binary operator: {:?}", bin.operator)),
+                };
+                let r = ctx.alloc_reg();
+                ctx.emit(opcode::encode(op, r, left, right));
+                Ok(r)
+            }
+            Expression::UnaryExpression(un) => {
+                let arg = self.emit_expression(&un.argument, ctx)?;
+                if matches!(un.operator, UnaryOperator::UnaryNegation) {
+                    let r = ctx.alloc_reg();
+                    ctx.emit(opcode::encode(OpCode::NEG, r, arg, 0));
+                    Ok(r)
+                } else {
+                    Err(format!("unsupported unary operator: {:?}", un.operator))
+                }
+            }
+            _ => Err(format!(
+                "unsupported expression type: {:?}",
+                std::mem::discriminant(expr)
+            )),
+        }
+    }
+}
diff --git a/crates/oxide_compiler/src/lib.rs b/crates/oxide_compiler/src/lib.rs
index 65ccf5d..00ab9d8 100644
--- a/crates/oxide_compiler/src/lib.rs
+++ b/crates/oxide_compiler/src/lib.rs
@@ -1,3 +1,5 @@
 #![doc = "OxideJS - AST to bytecode compiler"]
 
+pub mod compiler;
+pub mod module;
 pub mod opcode;
diff --git a/crates/oxide_compiler/src/module.rs b/crates/oxide_compiler/src/module.rs
new file mode 100644
index 0000000..daecd30
--- /dev/null
+++ b/crates/oxide_compiler/src/module.rs
@@ -0,0 +1,47 @@
+use std::fmt;
+
+use crate::compiler::Constant;
+use crate::opcode::{self, OpCode};
+
+pub struct CompiledModule {
+    pub bytecode: Vec<opcode::Instr>,
+    pub constants: Vec<Constant>,
+    pub n_registers: u8,
+}
+
+impl fmt::Display for CompiledModule {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        writeln!(f, "; n_registers = {}", self.n_registers)?;
+        writeln!(f, "; constants:")?;
+        for (i, c) in self.constants.iter().enumerate() {
+            writeln!(f, ";   [{i}] = {:?}", c)?;
+        }
+        writeln!(f)?;
+        for (offset, &instr) in self.bytecode.iter().enumerate() {
+            let op = opcode::opcode(instr);
+            let rd = opcode::rd(instr);
+            let a = opcode::a(instr);
+            let b = opcode::b(instr);
+            write!(f, "  {offset:04}  {op}")?;
+            match op {
+                OpCode::LOAD_CONST => {
+                    write!(f, " r{rd}, const[{}]", opcode::imm16(instr))?;
+                }
+                OpCode::JMP | OpCode::JMP_IF_FALSE | OpCode::JMP_IF_TRUE => {
+                    write!(f, " r{rd}, {offset:+}", offset = opcode::offset16(instr))?;
+                }
+                OpCode::RETURN | OpCode::HALT | OpCode::NOP => {
+                    write!(f, " r{rd}")?;
+                }
+                OpCode::NEG => {
+                    write!(f, " r{rd}, r{a}")?;
+                }
+                _ => {
+                    write!(f, " r{rd}, r{a}, r{b}")?;
+                }
+            }
+            writeln!(f)?;
+        }
+        Ok(())
+    }
+}