diff --git a/src/data/opcodes.c b/src/data/opcodes.c
new file mode 100644
index 0000000..f74f68a
--- /dev/null
+++ b/src/data/opcodes.c
@@ -0,0 +1,145 @@
+#include "opcodes.h"
+
+// clang-format off
+opcode_data_t *const opcodes[] = {
+    // RET
+    &(opcode_data_t) {
+        .mnemonic = "ret",
+        .opcode = 0xC3,
+        .opcode_extension = opcode_extension_none,
+        .operand_count = 0,
+    },
+    // RET imm16
+    &(opcode_data_t) {
+        .mnemonic = "ret",
+        .opcode = 0xC2,
+        .opcode_extension = opcode_extension_none,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_IMMEDIATE, .size = OPERAND_SIZE_16 },
+        },
+    },
+    // PUSH imm8
+    &(opcode_data_t) {
+        .mnemonic = "push",
+        .opcode = 0x6A,
+        .opcode_extension = opcode_extension_none,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_IMMEDIATE, .size = OPERAND_SIZE_8},
+        },
+    },
+    // PUSH imm16
+    &(opcode_data_t) {
+        .mnemonic = "push",
+        .opcode = 0x68,
+        .opcode_extension = opcode_extension_none,
+        .operand_size_prefix = true,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_IMMEDIATE, .size = OPERAND_SIZE_16},
+        },
+    },
+    // PUSH imm32
+    &(opcode_data_t) {
+        .mnemonic = "push",
+        .opcode = 0x68,
+        .opcode_extension = opcode_extension_none,
+        .operand_size_prefix = false,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_IMMEDIATE, .size = OPERAND_SIZE_32},
+        },
+    },
+    // PUSH reg16, 
+    &(opcode_data_t) {
+        .mnemonic = "push",
+        .opcode = 0x50,
+        .opcode_extension = opcode_extension_none,
+        .encoding_class = ENCODING_OPCODE_REGISTER,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_16 },
+        },
+    },
+    // PUSH reg64
+    &(opcode_data_t) {
+        .mnemonic = "push",
+        .opcode = 0x50,
+        .opcode_extension = opcode_extension_none,
+        .encoding_class = ENCODING_OPCODE_REGISTER,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_64 },
+        },
+    },
+    // NOT reg16
+    &(opcode_data_t) {
+        .mnemonic = "not",
+        .opcode = 0xF7,
+        .opcode_extension = 2,
+        .operand_size_prefix = true,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_16 },
+        },
+    },
+    // NOT reg32
+    &(opcode_data_t) {
+        .mnemonic = "not",
+        .opcode = 0xF7,
+        .opcode_extension = 2,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_32 },
+        },
+    },
+    // NOT reg64
+    &(opcode_data_t) {
+        .mnemonic = "not",
+        .opcode = 0xF7,
+        .opcode_extension = 2,
+        .rex_w_prefix = true,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_64 },
+        },
+    },
+
+    // NEG reg16
+    &(opcode_data_t) {
+        .mnemonic = "neg",
+        .opcode = 0xF7,
+        .opcode_extension = 3,
+        .operand_size_prefix = true,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_16 },
+        },
+    },
+    // NEG reg32
+    &(opcode_data_t) {
+        .mnemonic = "neg",
+        .opcode = 0xF7,
+        .opcode_extension = 3,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_32 },
+        },
+    },
+    // NEG reg64
+    &(opcode_data_t) {
+        .mnemonic = "neg",
+        .opcode = 0xF7,
+        .opcode_extension = 3,
+        .rex_w_prefix = true,
+        .operand_count = 1,
+        .operands = {
+            { .kind = OPERAND_REGISTER, .size = OPERAND_SIZE_64 },
+        },
+    },
+
+
+    nullptr,
+};
+
diff --git a/src/data/opcodes.h b/src/data/opcodes.h
new file mode 100644
index 0000000..14c842b
--- /dev/null
+++ b/src/data/opcodes.h
@@ -0,0 +1,56 @@
+#ifndef INCLUDE_DATA_OPCODES_H_
+#define INCLUDE_DATA_OPCODES_H_
+
+#include "../data/registers.h"
+#include <stddef.h>
+#include <stdint.h>
+
+constexpr uint8_t rex_prefix = 0x40;
+constexpr uint8_t rex_prefix_w = 0x48;
+constexpr uint8_t rex_prefix_r = 0x44;
+constexpr uint8_t rex_prefix_x = 0x42;
+constexpr uint8_t rex_prefix_b = 0x41;
+
+constexpr uint8_t operand_size_prefix = 0x66;
+constexpr uint8_t memory_size_prefix = 0x67;
+constexpr uint8_t lock_prefix = 0xF0;
+constexpr uint8_t repne_prefix = 0xF2;
+constexpr uint8_t rep_prefix = 0xF3;
+
+typedef enum encoding_class {
+    ENCODING_DEFAULT,         // use modrm+sib for registers and memory, append
+                              // immediates
+    ENCODING_OPCODE_REGISTER, // encode the register in the last 3 bits of the
+                              // opcode
+} encoding_class_t;
+
+typedef enum operand_kind {
+    OPERAND_REGISTER,
+    OPERAND_MEMORY,
+    OPERAND_IMMEDIATE,
+} operand_kind_t;
+
+typedef struct operand_info {
+    operand_kind_t kind;
+    operand_size_t size;
+} operand_info_t;
+
+constexpr uint8_t opcode_extension_none = 0xFF;
+
+typedef struct opcode_data {
+    const char *mnemonic;
+
+    uint16_t opcode;
+    uint8_t opcode_extension; // 3 bits for the opcode extension in the reg
+                              // field of a modr/m byte
+    encoding_class_t encoding_class;
+    bool operand_size_prefix;
+    bool address_size_prefix;
+    bool rex_w_prefix;
+    size_t operand_count;
+    operand_info_t operands[3];
+} opcode_data_t;
+
+extern opcode_data_t *const opcodes[];
+
+#endif // INCLUDE_DATA_OPCODES_H_