diff --git a/src/disassembler.c b/src/disassembler.c
index 0575be1..5be17e6 100644
--- a/src/disassembler.c
+++ b/src/disassembler.c
@@ -1,7 +1,82 @@
-/* Copyright (C) 2014-2015 Ben Kurtovic <ben.kurtovic@gmail.com>
+/* Copyright (C) 2014-2016 Ben Kurtovic <ben.kurtovic@gmail.com>
    Released under the terms of the MIT License. See LICENSE for details. */
 
 #include "disassembler.h"
+#include "disassembler/mnemonics.h"
+#include "disassembler/sizes.h"
+#include "util.h"
+
+/*
+    Format a sequence of bytes of a certain length as a pretty string.
+
+    The result must be freed by the caller.
+*/
+static char* format_bytestring(const uint8_t *bytes, size_t size)
+{
+    if (!size)
+        return NULL;
+
+    char *str = cr_malloc(sizeof(char) * (3 * size));
+    size_t i;
+
+    for (i = 0; i < size; i++) {
+        snprintf(&str[3 * i], 3, "%02X", bytes[i]);
+        str[3 * i + 2] = ' ';
+    }
+    str[3 * size - 1] = '\0';
+    return str;
+}
+
+/*
+    Extract the arguments for the given instruction.
+
+    The return value must be free()d.
+*/
+static char* decode_argument(const uint8_t *bytes)
+{
+    // TODO
+    (void) bytes;
+    return NULL;
+}
+
+/*
+    Free the given DisasInstr struct.
+*/
+void disas_instr_free(DisasInstr *instr)
+{
+    free(instr->bytestr);
+    free(instr->line);
+    free(instr);
+}
+
+/*
+    Disassemble a single instruction starting at the given address.
+
+    Return a dynamically allocated structure containing various interesting
+    fields. This must be freed by the user with disas_instr_free().
+*/
+DisasInstr* disassemble_instruction(const uint8_t *bytes)
+{
+    size_t size = get_instr_size(bytes);
+    char *bytestr = format_bytestring(bytes, size);
+    char *mnemonic = decode_mnemonic(bytes);
+    char *arg = decode_argument(bytes);
+    char *line;
+
+    if (arg) {
+        line = cr_malloc(strlen(mnemonic) + strlen(arg) + 2);
+        sprintf(line, "%s\t%s", mnemonic, arg);
+        free(arg);
+    } else {
+        line = cr_strdup(mnemonic);
+    }
+
+    DisasInstr *instr = cr_malloc(sizeof(DisasInstr));
+    instr->size = size;
+    instr->bytestr = bytestr;
+    instr->line = line;
+    return instr;
+}
 
 /*
     Disassemble the binary file at the input path into z80 source code.
diff --git a/src/disassembler.h b/src/disassembler.h
index d56db3e..a4715d8 100644
--- a/src/disassembler.h
+++ b/src/disassembler.h
@@ -1,14 +1,26 @@
-/* Copyright (C) 2014-2015 Ben Kurtovic <ben.kurtovic@gmail.com>
+/* Copyright (C) 2014-2016 Ben Kurtovic <ben.kurtovic@gmail.com>
    Released under the terms of the MIT License. See LICENSE for details. */
 
 #pragma once
 
 #include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
 
 /* Structs */
 
-// ...
+typedef struct {
+    size_t size;
+    char *bytestr;
+    char *line;
+} DisasInstr;
+
+// typedef struct { ... } Disassembly;
 
 /* Functions */
 
+void disas_instr_free(DisasInstr*);
+
+DisasInstr* disassemble_instruction(const uint8_t*);
+// Disassembly* disassemble(const uint8_t*);  // TODO
 bool disassemble_file(const char*, const char*);
diff --git a/src/disassembler/mnemonics.c b/src/disassembler/mnemonics.c
new file mode 100644
index 0000000..ff5cf44
--- /dev/null
+++ b/src/disassembler/mnemonics.c
@@ -0,0 +1,49 @@
+/* Copyright (C) 2014-2016 Ben Kurtovic <ben.kurtovic@gmail.com>
+   Released under the terms of the MIT License. See LICENSE for details. */
+
+#include "mnemonics.h"
+
+static char* instr_mnemonics[256] = {
+    /* 00 */ "nop",  "ld",   "ld",   "inc",  "inc",  "dec",  "ld",   "rlca",
+    /* 08 */ "ex",   "add",  "ld",   "dec",  "inc",  "dec",  "ld",   "rrca",
+    /* 10 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 18 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 20 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 28 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 30 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 38 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 40 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 48 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 50 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 58 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 60 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 68 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 70 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 78 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 80 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 88 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 90 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* 98 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* A0 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* A8 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* B0 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* B8 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* C0 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* C8 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* D0 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* D8 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* E0 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* E8 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* F0 */ "????", "????", "????", "????", "????", "????", "????", "????",
+    /* F8 */ "????", "????", "????", "????", "????", "????", "????", "????"
+};
+
+/*
+    Extract the assembly mnemonic for the given opcode.
+
+    The return value is a string literal and should not be freed.
+*/
+char* decode_mnemonic(const uint8_t *bytes)
+{
+    return instr_mnemonics[bytes[0]];  // TODO: extended...
+}
diff --git a/src/disassembler/mnemonics.h b/src/disassembler/mnemonics.h
new file mode 100644
index 0000000..82d8084
--- /dev/null
+++ b/src/disassembler/mnemonics.h
@@ -0,0 +1,10 @@
+/* Copyright (C) 2014-2016 Ben Kurtovic <ben.kurtovic@gmail.com>
+   Released under the terms of the MIT License. See LICENSE for details. */
+
+#pragma once
+
+#include <stdint.h>
+
+/* Functions */
+
+char* decode_mnemonic(const uint8_t*);
diff --git a/src/disassembler/sizes.c b/src/disassembler/sizes.c
new file mode 100644
index 0000000..1941ae2
--- /dev/null
+++ b/src/disassembler/sizes.c
@@ -0,0 +1,118 @@
+/* Copyright (C) 2014-2016 Ben Kurtovic <ben.kurtovic@gmail.com>
+   Released under the terms of the MIT License. See LICENSE for details. */
+
+#include "sizes.h"
+
+static size_t instr_sizes[256] = {
+    1, 3, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1,
+    2, 3, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 2, 1,
+    2, 3, 3, 1, 1, 1, 2, 1, 2, 1, 3, 1, 1, 1, 2, 1,
+    2, 3, 3, 1, 1, 1, 2, 1, 2, 1, 3, 1, 1, 1, 2, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 3, 3, 3, 1, 2, 1, 1, 1, 3, 0, 3, 3, 2, 1,
+    1, 1, 3, 2, 3, 1, 2, 1, 1, 1, 3, 2, 3, 0, 2, 1,
+    1, 1, 3, 1, 3, 1, 2, 1, 1, 1, 3, 1, 3, 0, 2, 1,
+    1, 1, 3, 1, 3, 1, 2, 1, 1, 1, 3, 1, 3, 0, 2, 1
+};
+
+static size_t instr_sizes_extended[256] = {
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 4, 2, 2, 2, 2, 2, 2, 2, 4, 2, 2, 2, 2,
+    2, 2, 2, 4, 2, 2, 2, 2, 2, 2, 2, 4, 2, 2, 2, 2,
+    2, 2, 2, 4, 2, 2, 2, 2, 2, 2, 2, 4, 2, 2, 2, 2,
+    2, 2, 2, 4, 2, 2, 2, 2, 2, 2, 2, 4, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
+};
+
+static size_t instr_sizes_bits[256] = {
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
+};
+
+static size_t instr_sizes_index[256] = {
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 4, 4, 2, 2, 2, 3, 2, 2, 2, 4, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 3, 3, 4, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2,
+    3, 3, 3, 3, 3, 3, 2, 3, 2, 2, 2, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
+};
+
+static size_t instr_sizes_index_bits[256] = {
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4
+};
+
+/*
+    Return the byte length of the instruction starting at the given address.
+*/
+size_t get_instr_size(const uint8_t *bytes)
+{
+    uint8_t b = bytes[0];
+
+    if (b == 0xED)
+        return instr_sizes_extended[bytes[1]];
+    if (b == 0xCB)
+        return instr_sizes_bits[bytes[1]];
+    if (b == 0xDD || b == 0xFD) {
+        if (bytes[1] == 0xCB)
+            return instr_sizes_index_bits[bytes[2]];
+        return instr_sizes_index[bytes[1]];
+    }
+    return instr_sizes[b];
+}
diff --git a/src/disassembler/sizes.h b/src/disassembler/sizes.h
new file mode 100644
index 0000000..01949e3
--- /dev/null
+++ b/src/disassembler/sizes.h
@@ -0,0 +1,11 @@
+/* Copyright (C) 2014-2016 Ben Kurtovic <ben.kurtovic@gmail.com>
+   Released under the terms of the MIT License. See LICENSE for details. */
+
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+/* Functions */
+
+size_t get_instr_size(const uint8_t*);
diff --git a/src/mmu.c b/src/mmu.c
index bb9e2a5..2aa491f 100644
--- a/src/mmu.c
+++ b/src/mmu.c
@@ -161,3 +161,15 @@ bool mmu_write_byte(MMU *mmu, uint16_t addr, uint8_t value)
         return true;
     }
 }
+
+/*
+    Read four bytes of memory from the given address.
+*/
+uint32_t mmu_read_quad(MMU *mmu, uint16_t addr)
+{
+    return (
+         mmu_read_byte(mmu, addr) +
+        (mmu_read_byte(mmu, addr + 1) <<  8) +
+        (mmu_read_byte(mmu, addr + 2) << 16) +
+        (mmu_read_byte(mmu, addr + 3) << 24));
+}
diff --git a/src/mmu.h b/src/mmu.h
index 3ee4088..a91669a 100644
--- a/src/mmu.h
+++ b/src/mmu.h
@@ -28,3 +28,4 @@ void mmu_load_rom(MMU*, const uint8_t*, size_t);
 void mmu_power(MMU*);
 uint8_t mmu_read_byte(MMU*, uint16_t);
 bool mmu_write_byte(MMU*, uint16_t, uint8_t);
+uint32_t mmu_read_quad(MMU*, uint16_t);
diff --git a/src/z80.c b/src/z80.c
index b3a45bd..f951ca8 100644
--- a/src/z80.c
+++ b/src/z80.c
@@ -169,8 +169,12 @@ static inline void increment_refresh_counter(Z80 *z80)
 */
 static inline void trace_instruction(const Z80 *z80)
 {
-    TRACE("PC @ 0x%04X", z80->regfile.pc)
-    // TODO
+    uint32_t quad = mmu_read_quad(z80->mmu, z80->regfile.pc);
+    uint8_t bytes[4] = {quad, quad >> 8, quad >> 16, quad >> 24};
+    DisasInstr *instr = disassemble_instruction(bytes);
+
+    TRACE("0x%04X:  %11s    %s", z80->regfile.pc, instr->bytestr, instr->line)
+    disas_instr_free(instr);
 }
 
 /*
@@ -185,9 +189,9 @@ bool z80_do_cycles(Z80 *z80, double cycles)
     cycles -= z80->pending_cycles;
     while (cycles > 0 && !z80->except) {
         uint8_t opcode = mmu_read_byte(z80->mmu, z80->regfile.pc);
+        increment_refresh_counter(z80);
         if (TRACE_LEVEL)
             trace_instruction(z80);
-        increment_refresh_counter(z80);
         cycles -= (*instruction_lookup_table[opcode])(z80, opcode);
     }