diff --git a/src/cpu/mod.rs b/src/cpu/mod.rs
index 616ac7d..c2340c3 100644
--- a/src/cpu/mod.rs
+++ b/src/cpu/mod.rs
@@ -2,6 +2,7 @@ mod execute;
 mod fetch;
 mod registers;
 use crate::memory::{ActiveInterrupt, Memory, SystemInfo};
+use crate::trace::{CpuTrace, TraceHandler};
 use execute::Execute;
 use fetch::Fetch;
 use registers::{flags, Registers};
@@ -23,6 +24,7 @@ pub struct Mos6502 {
   cycle_count: u64,
   cycles_since_poll: u32,
   variant: Mos6502Variant,
+  trace: Option<Box<dyn TraceHandler>>,
 }
 
 /// Read and write from the system's memory.
@@ -142,9 +144,14 @@ impl Mos6502 {
       cycle_count: 0,
       cycles_since_poll: 0,
       variant,
+      trace: None,
     }
   }
 
+  pub fn attach_trace_handler(&mut self, trace: Box<dyn TraceHandler>) {
+    self.trace = Some(trace);
+  }
+
   pub fn reset(&mut self) {
     self.memory.reset();
     self.registers.reset();
@@ -162,6 +169,15 @@ impl Mos6502 {
   /// Execute a single instruction.
   pub fn tick(&mut self) -> u8 {
     let opcode = self.fetch();
+
+    if let Some(handler) = &mut self.trace {
+      let trace = CpuTrace {
+        opcode,
+        address: self.registers.pc.address() - 1,
+      };
+      handler.handle(&trace);
+    }
+
     match self.execute(opcode) {
       Ok(cycles) => {
         self.cycle_count += cycles as u64;
diff --git a/src/lib.rs b/src/lib.rs
index d4fe3ee..401f648 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -31,6 +31,9 @@ pub mod roms;
 /// Systems are created by a [`systems::SystemBuilder`]. A system is created with some roms, configuration, and platform. For instance, the `build` implementation on [`systems::pet::PetSystemBuilder`] takes in [`systems::pet::PetSystemRoms`], [`systems::pet::PetSystemConfig`], and an `Arc<dyn PlatformProvider>`.
 pub mod systems;
 
+/// Traces log the state of the system as it runs (e.g., to a file). This is useful for debugging.
+pub mod trace;
+
 mod time;
 
 #[cfg(target_arch = "wasm32")]
diff --git a/src/main.rs b/src/main.rs
index 77c4e01..978d588 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -51,11 +51,16 @@ struct Args {
 
   #[clap(short, long, value_parser, default_value = "symbolic")]
   key_mapping: KeyMappingArg,
+
+  #[clap(short, long, value_parser, default_value = "false")]
+  trace: bool,
 }
 
 #[cfg(not(target_arch = "wasm32"))]
 fn main() {
-  use libnoentiendo::{cpu::Mos6502Variant, systems::klaus::KlausSystemConfig};
+  use libnoentiendo::{
+    cpu::Mos6502Variant, systems::klaus::KlausSystemConfig, trace::file::FileTraceHandler,
+  };
 
   let args = Args::parse();
 
@@ -74,7 +79,7 @@ fn main() {
     KeyMappingArg::Physical => KeyMappingStrategy::Physical,
   };
 
-  let system = match args.system {
+  let mut system = match args.system {
     SystemArg::Basic => BasicSystemBuilder::build(romfile.unwrap(), (), platform.provider()),
     SystemArg::Easy => Easy6502SystemBuilder::build(romfile.unwrap(), (), platform.provider()),
     SystemArg::Klaus => KlausSystemBuilder::build(
@@ -105,5 +110,9 @@ fn main() {
     ),
   };
 
+  if args.trace {
+    system.attach_trace_handler(Box::new(FileTraceHandler::new("./cpu.trace".to_owned())));
+  }
+
   platform.run(system);
 }
diff --git a/src/systems/basic.rs b/src/systems/basic.rs
index f4e90fc..a6c9a81 100644
--- a/src/systems/basic.rs
+++ b/src/systems/basic.rs
@@ -6,6 +6,7 @@ use crate::memory::{BlockMemory, BranchMemory};
 use crate::platform::{PlatformProvider, WindowConfig};
 use crate::roms::RomFile;
 use crate::systems::{System, SystemBuilder};
+use crate::trace::TraceHandler;
 use std::io::Write;
 use std::sync::Arc;
 
@@ -91,6 +92,10 @@ pub struct BasicSystem {
 }
 
 impl System for BasicSystem {
+  fn attach_trace_handler(&mut self, handler: Box<dyn TraceHandler>) {
+    self.cpu.attach_trace_handler(handler);
+  }
+
   fn tick(&mut self) -> Duration {
     Duration::from_secs_f64(1.0 / 20_000.0) * self.cpu.tick().into()
   }
diff --git a/src/systems/c64/mod.rs b/src/systems/c64/mod.rs
index 5670a09..bfddc59 100644
--- a/src/systems/c64/mod.rs
+++ b/src/systems/c64/mod.rs
@@ -16,6 +16,7 @@ use crate::{
   },
   platform::{PlatformProvider, WindowConfig},
   systems::System,
+  trace::TraceHandler,
 };
 
 mod keyboard;
@@ -316,6 +317,10 @@ pub struct C64System {
 }
 
 impl System for C64System {
+  fn attach_trace_handler(&mut self, handler: Box<dyn TraceHandler>) {
+    self.cpu.attach_trace_handler(handler);
+  }
+
   fn tick(&mut self) -> Duration {
     Duration::from_secs_f64(1.0 / 1_000_000.0) * self.cpu.tick() as u32
   }
diff --git a/src/systems/easy.rs b/src/systems/easy.rs
index a4ca918..67eb5fc 100644
--- a/src/systems/easy.rs
+++ b/src/systems/easy.rs
@@ -6,6 +6,7 @@ use crate::memory::{ActiveInterrupt, BlockMemory, BranchMemory, Memory, SystemIn
 use crate::platform::{Color, PlatformProvider, WindowConfig};
 use crate::roms::RomFile;
 use crate::systems::{System, SystemBuilder};
+use crate::trace::TraceHandler;
 use std::sync::Arc;
 
 const WIDTH: u32 = 32;
@@ -92,6 +93,10 @@ pub struct Easy6502System {
 }
 
 impl System for Easy6502System {
+  fn attach_trace_handler(&mut self, handler: Box<dyn TraceHandler>) {
+    self.cpu.attach_trace_handler(handler);
+  }
+
   fn tick(&mut self) -> Duration {
     Duration::from_secs_f64(1.0 / 20_000.0) * self.cpu.tick().into()
   }
diff --git a/src/systems/klaus.rs b/src/systems/klaus.rs
index a43f1d9..91b0206 100644
--- a/src/systems/klaus.rs
+++ b/src/systems/klaus.rs
@@ -5,6 +5,7 @@ use crate::memory::BlockMemory;
 use crate::platform::{PlatformProvider, WindowConfig};
 use crate::roms::RomFile;
 use crate::systems::System;
+use crate::trace::TraceHandler;
 use std::cell::Cell;
 use std::rc::Rc;
 use std::sync::Arc;
@@ -44,6 +45,10 @@ pub struct KlausSystem {
 }
 
 impl System for KlausSystem {
+  fn attach_trace_handler(&mut self, handler: Box<dyn TraceHandler>) {
+    self.cpu.attach_trace_handler(handler);
+  }
+
   fn tick(&mut self) -> Duration {
     self.cpu.tick();
     if let Some(pc) = &self.pc {
diff --git a/src/systems/mod.rs b/src/systems/mod.rs
index ad2c153..1bc60b9 100644
--- a/src/systems/mod.rs
+++ b/src/systems/mod.rs
@@ -1,4 +1,7 @@
-use crate::platform::{PlatformProvider, WindowConfig};
+use crate::{
+  platform::{PlatformProvider, WindowConfig},
+  trace::TraceHandler,
+};
 use instant::Duration;
 use std::sync::Arc;
 
@@ -21,6 +24,9 @@ pub trait SystemBuilder<SystemType, RomRegistry, SystemConfig> {
 
 /// A representation of an emulated system.
 pub trait System {
+  /// Attach a trace handler to the CPU in this sytem.
+  fn attach_trace_handler(&mut self, handler: Box<dyn TraceHandler>);
+
   /// Advance the system by one tick.
   fn tick(&mut self) -> Duration;
 
diff --git a/src/systems/pet/mod.rs b/src/systems/pet/mod.rs
index 222f043..d81af1f 100644
--- a/src/systems/pet/mod.rs
+++ b/src/systems/pet/mod.rs
@@ -4,6 +4,7 @@ use crate::memory::mos652x::{Pia, Via};
 use crate::memory::{BlockMemory, BranchMemory, NullMemory, NullPort, Port, SystemInfo};
 use crate::platform::{Color, PlatformProvider, WindowConfig};
 use crate::systems::{System, SystemBuilder};
+use crate::trace::TraceHandler;
 use instant::Instant;
 use std::cell::Cell;
 use std::rc::Rc;
@@ -210,6 +211,10 @@ pub struct PetSystem {
 }
 
 impl System for PetSystem {
+  fn attach_trace_handler(&mut self, handler: Box<dyn TraceHandler>) {
+    self.cpu.attach_trace_handler(handler);
+  }
+
   fn tick(&mut self) -> Duration {
     Duration::from_secs_f64(1.0 / 1_000_000.0) * self.cpu.tick() as u32
   }
diff --git a/src/systems/vic/mod.rs b/src/systems/vic/mod.rs
index 8293a53..8151e0b 100644
--- a/src/systems/vic/mod.rs
+++ b/src/systems/vic/mod.rs
@@ -9,6 +9,7 @@ use crate::memory::{BlockMemory, BranchMemory, NullMemory, NullPort, Port, Syste
 use crate::platform::{PlatformProvider, WindowConfig};
 use crate::roms::RomFile;
 use crate::systems::System;
+use crate::trace::TraceHandler;
 use std::cell::{Cell, RefCell};
 use std::rc::Rc;
 use std::sync::Arc;
@@ -311,6 +312,10 @@ pub struct Vic20System {
 }
 
 impl System for Vic20System {
+  fn attach_trace_handler(&mut self, handler: Box<dyn TraceHandler>) {
+    self.cpu.attach_trace_handler(handler);
+  }
+
   fn tick(&mut self) -> instant::Duration {
     Duration::from_secs_f64(1.0 / 1_000_000.0) * self.cpu.tick() as u32
   }
diff --git a/src/trace/file.rs b/src/trace/file.rs
new file mode 100644
index 0000000..d9ecf38
--- /dev/null
+++ b/src/trace/file.rs
@@ -0,0 +1,23 @@
+use crate::trace::{CpuTrace, TraceHandler};
+use std::{fs::File, io::Write};
+
+pub struct FileTraceHandler {
+  file: File,
+}
+
+impl FileTraceHandler {
+  pub fn new(filename: String) -> Self {
+    Self {
+      file: File::create(filename).expect("Invalid filename"),
+    }
+  }
+}
+
+impl TraceHandler for FileTraceHandler {
+  fn handle(&mut self, trace: &CpuTrace) {
+    self
+      .file
+      .write(format!("{:04X}: {:02X}\n", trace.address, trace.opcode).as_bytes())
+      .unwrap();
+  }
+}
diff --git a/src/trace/mod.rs b/src/trace/mod.rs
new file mode 100644
index 0000000..2ace167
--- /dev/null
+++ b/src/trace/mod.rs
@@ -0,0 +1,14 @@
+#[cfg(not(target_arch = "wasm32"))]
+pub mod file;
+
+/// Trace information provided after each instruction by the CPU.
+pub struct CpuTrace {
+  pub address: u16,
+  pub opcode: u8,
+}
+
+/// An item which can handle a CPU trace (e.g. logging to a file)
+pub trait TraceHandler {
+  /// Handle a trace event.
+  fn handle(&mut self, trace: &CpuTrace);
+}