diff --git a/src/common.h b/src/common.h
index e5224fd..98d48b6 100644
--- a/src/common.h
+++ b/src/common.h
@@ -6,5 +6,6 @@
 #include <stdint.h>
 
 #define DEBUG_TRACE_EXECUTION
+#define DEBUG_PRINT_CODE
 
 #endif
diff --git a/src/compiler.c b/src/compiler.c
new file mode 100644
index 0000000..82c316d
--- /dev/null
+++ b/src/compiler.c
@@ -0,0 +1,250 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "common.h"
+#include "compiler.h"
+#include "scanner.h"
+
+#ifdef DEBUG_PRINT_CODE
+#include "debug.h"
+#endif
+
+typedef struct {
+  Token current;
+  Token previous;
+  bool hadError;
+  bool panicMode;
+} Parser;
+
+typedef enum {
+  PREC_NONE,
+  PREC_ASSIGNMENT,  // =
+  PREC_OR,          // or
+  PREC_AND,         // and
+  PREC_EQUALITY,    // == !=
+  PREC_COMPARISON,  // < > <= >=
+  PREC_TERM,        // + -
+  PREC_FACTOR,      // * /
+  PREC_UNARY,       // ! -
+  PREC_CALL,        // . ()
+  PREC_PRIMARY
+} Precedence;
+
+typedef void (*ParseFn)();
+
+typedef struct {
+  ParseFn prefix;
+  ParseFn infix;
+  Precedence precedence;
+} ParseRule;
+
+Parser parser;
+Chunk* compilingChunk;
+
+static Chunk* currentChunk() {
+  return compilingChunk;
+}
+
+static void errorAt(Token* token, const char* message) {
+  if (parser.panicMode) return;
+  parser.panicMode = true;
+  fprintf(stderr, "[line %d] Error", token->line);
+
+  if (token->type == TOKEN_EOF) {
+    fprintf(stderr, " at end");
+  } else if (token->type == TOKEN_ERROR) {
+    // Nothing.
+  } else {
+    fprintf(stderr, " at '%.*s'", token->length, token->start);
+  }
+
+  fprintf(stderr, ": %s\n", message);
+  parser.hadError = true;
+}
+
+static void error(const char* message) {
+  errorAt(&parser.previous, message);
+}
+
+static void errorAtCurrent(const char* message) {
+  errorAt(&parser.current, message);
+}
+
+static void advance() {
+  parser.previous = parser.current;
+
+  for (;;) {
+    parser.current = scanToken();
+    if (parser.current.type != TOKEN_ERROR) break;
+
+    errorAtCurrent(parser.current.start);
+  }
+}
+
+static void consume(TokenType type, const char* message) {
+  if (parser.current.type == type) {
+    advance();
+    return;
+  }
+
+  errorAtCurrent(message);
+}
+
+static void emitByte(uint8_t byte) {
+  writeChunk(currentChunk(), byte, parser.previous.line);
+}
+
+static void emitBytes(uint8_t byte1, uint8_t byte2) {
+  emitByte(byte1);
+  emitByte(byte2);
+}
+
+static void emitReturn() {
+  emitByte(OP_RETURN);
+}
+
+static uint8_t makeConstant(Value value) {
+  int constant = addConstant(currentChunk(), value);
+  if (constant > UINT8_MAX) {
+    error("Too many constants in one chunk.");
+    return 0;
+  }
+
+  return (uint8_t)constant;
+}
+
+static void emitConstant(Value value) {
+  emitBytes(OP_CONSTANT, makeConstant(value));
+}
+
+static void endCompiler() {
+  emitReturn();
+#ifdef DEBUG_PRINT_CODE
+  if (!parser.hadError) {
+    disassembleChunk(currentChunk(), "code");
+  }
+#endif
+}
+
+static void expression();
+static ParseRule* getRule(TokenType type);
+static void parsePrecedence(Precedence precedence);
+
+static void expression() {
+  parsePrecedence(PREC_ASSIGNMENT);
+}
+
+static void grouping() {
+  expression();
+  consume(TOKEN_RIGHT_PAREN, "Expect ')' after expression.");
+}
+
+static void number() {
+  double value = strtod(parser.previous.start, NULL);
+  emitConstant(value);
+}
+
+static void binary() {
+  TokenType operatorType = parser.previous.type;
+  ParseRule* rule = getRule(operatorType);
+  parsePrecedence((Precedence)(rule->precedence + 1));
+
+  switch (operatorType) {
+    case TOKEN_PLUS:          emitByte(OP_ADD); break;
+    case TOKEN_MINUS:         emitByte(OP_SUBTRACT); break;
+    case TOKEN_STAR:          emitByte(OP_MULTIPLY); break;
+    case TOKEN_SLASH:         emitByte(OP_DIVIDE); break;
+    default: return; // Unreachable.
+  }
+}
+
+static void unary() {
+  TokenType operatorType = parser.previous.type;
+
+  // Compile the operand.
+  parsePrecedence(PREC_UNARY);
+
+  // Emit the operator instruction.
+  switch (operatorType) {
+    case TOKEN_MINUS: emitByte(OP_NEGATE); break;
+    default: return; // Unreachable.
+  }
+}
+
+ParseRule rules[] = {
+  [TOKEN_LEFT_PAREN]    = {grouping, NULL,   PREC_NONE},
+  [TOKEN_RIGHT_PAREN]   = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_LEFT_BRACE]    = {NULL,     NULL,   PREC_NONE}, 
+  [TOKEN_RIGHT_BRACE]   = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_COMMA]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_DOT]           = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_MINUS]         = {unary,    binary, PREC_TERM},
+  [TOKEN_PLUS]          = {NULL,     binary, PREC_TERM},
+  [TOKEN_SEMICOLON]     = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_SLASH]         = {NULL,     binary, PREC_FACTOR},
+  [TOKEN_STAR]          = {NULL,     binary, PREC_FACTOR},
+  [TOKEN_BANG]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_BANG_EQUAL]    = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_EQUAL]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_EQUAL_EQUAL]   = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_GREATER]       = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_GREATER_EQUAL] = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_LESS]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_LESS_EQUAL]    = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_IDENTIFIER]    = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_STRING]        = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_NUMBER]        = {number,   NULL,   PREC_NONE},
+  [TOKEN_AND]           = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_TYPE]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_ELSE]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_FALSE]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_FOR]           = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_FN]            = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_IF]            = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_NIL]           = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_OR]            = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_PRINT]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_RETURN]        = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_SUPER]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_THIS]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_TRUE]          = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_LET]           = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_WHILE]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_ERROR]         = {NULL,     NULL,   PREC_NONE},
+  [TOKEN_EOF]           = {NULL,     NULL,   PREC_NONE},
+};
+
+static ParseRule* getRule(TokenType type) {
+  return &rules[type];
+}
+
+static void parsePrecedence(Precedence precedence) {
+  advance();
+  ParseFn prefixRule = getRule(parser.previous.type)->prefix;
+  if (prefixRule == NULL) {
+    error("Expect expression.");
+    return;
+  }
+
+  prefixRule();
+
+  while (precedence <= getRule(parser.current.type)->precedence) {
+    advance();
+    ParseFn infixRule = getRule(parser.previous.type)->infix;
+    infixRule();
+  }
+}
+
+bool compile(const char* source, Chunk* chunk) {
+  newScanner(source);
+  compilingChunk = chunk;
+
+  parser.hadError = false;
+  parser.panicMode = false;
+
+  advance();
+  expression();
+  consume(TOKEN_EOF, "Expect end of expression.");
+  endCompiler();
+  return !parser.hadError;
+}
diff --git a/src/compiler.h b/src/compiler.h
new file mode 100644
index 0000000..67eb4d0
--- /dev/null
+++ b/src/compiler.h
@@ -0,0 +1,9 @@
+#ifndef ztl_compiler_h
+#define ztl_compiler_h
+
+#include "vm.h"
+
+bool compile(const char* source, Chunk* chunk);
+
+#endif
+
diff --git a/src/main.c b/src/main.c
index ec32b79..5f73ee6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,36 +1,77 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
 #include "common.h"
 #include "chunk.h"
 #include "debug.h"
 #include "vm.h"
 
-int main(int argc, const char** argv) {
+static void repl() {
+  char line[1024];
+  for (;;) {
+    printf("> ");
+
+    if (!fgets(line, sizeof(line), stdin)) {
+      printf("\n");
+      break;
+    }
+
+    interpret(line);
+  }
+}
+
+static char *readFile(const char *path) {
+  FILE *file = fopen(path, "rb");
+  if (file == NULL) {
+    fprintf(stderr, "Could not open file \"%s\".\n", path);
+    exit(74);
+  }
+
+  fseek(file, 0L, SEEK_END);
+  size_t fileSize = ftell(file);
+  rewind(file);
+
+  char *buffer = (char*)malloc(fileSize + 1);
+  if (buffer == NULL) {
+    fprintf(stderr, "Not enough memory to read \"%s\".\n", path);
+    exit(74);
+  }
+
+  size_t bytesRead = fread(buffer, sizeof(char), fileSize, file);
+  if (bytesRead < fileSize) {
+    fprintf(stderr, "Could not read file \"%s\".\n", path);
+    exit(74);
+  }
+
+  buffer[bytesRead] = '\0';
+
+  fclose(file);
+  return buffer;
+}
+
+static void runFile(const char *path) {
+  char *source = readFile(path);
+  InterpretResult result = interpret(source);
+  free(source); 
+
+  if (result == INTERPRET_COMPILE_ERROR) exit(65);
+  if (result == INTERPRET_RUNTIME_ERROR) exit(70);
+}
+
+int main(int argc, const char* *argv) {
   newVM();
   
-  Chunk chunk;
-  newChunk(&chunk);
+  if (argc == 1) {
+    repl();
+  } else if (argc == 2) {
+    runFile(argv[1]);
+  } else {
+    fprintf(stderr, "Usage: clox [path]\n");
+    exit(64);
+  }
 
-  int constant = addConstant(&chunk, 1.2);
-  writeChunk(&chunk, OP_CONSTANT, 123);
-  writeChunk(&chunk, constant, 123);
-
-  constant = addConstant(&chunk, 3.4);
-  writeChunk(&chunk, OP_CONSTANT, 123);
-  writeChunk(&chunk, constant, 123);
-
-  writeChunk(&chunk, OP_ADD, 123);
-
-  constant = addConstant(&chunk, 5.6);
-  writeChunk(&chunk, OP_CONSTANT, 123);
-  writeChunk(&chunk, constant, 123);
-
-  writeChunk(&chunk, OP_DIVIDE, 123);
-  writeChunk(&chunk, OP_NEGATE, 123);
-
-  writeChunk(&chunk, OP_RETURN, 1);
-
-  disassembleChunk(&chunk, "test chunk");
   freeVM();
-  freeChunk(&chunk);
   return 0;
 }
 
diff --git a/src/scanner.c b/src/scanner.c
new file mode 100644
index 0000000..505167d
--- /dev/null
+++ b/src/scanner.c
@@ -0,0 +1,240 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "common.h"
+#include "scanner.h"
+
+typedef struct {
+  const char *start;
+  const char *current;
+  int line;
+} Scanner;
+
+Scanner scanner;
+
+void newScanner(const char* source) {
+  scanner.start = source;
+  scanner.current = source;
+  scanner.line = 1;
+}
+
+static Token newToken(TokenType type) {
+  Token token;
+  token.type = type;
+  token.start = scanner.start;
+  token.length = (int)(scanner.current - scanner.start);
+  token.line = scanner.line;
+  return token;
+}
+
+static Token errorToken(const char* message) {
+  Token token;
+  token.type = TOKEN_ERROR;
+  token.start = message;
+  token.length = (int)strlen(message);
+  token.line = scanner.line;
+  return token;
+}
+
+static bool isAtEnd() {
+  return *scanner.current == '\0';
+}
+
+static char peek() {
+  return *scanner.current;
+}
+
+static char peekNext() {
+  if (isAtEnd()) return '\0';
+  return scanner.current[1];
+}
+
+static char advance() {
+  scanner.current++;
+  return scanner.current[-1];
+}
+
+static bool match(char expected) {
+  if (isAtEnd()) return false;
+  if (*scanner.current != expected) return false;
+  scanner.current++;
+  return true;
+}
+
+static void skipWhitespace() {
+  for (;;) {
+    char c = peek();
+    switch (c) {
+      case ' ':
+      case '\r':
+      case '\t':
+        advance();
+        break;
+      case '\n':
+        scanner.line++;
+        advance();
+        break;
+      case '/':
+        if (peekNext() == '/') {
+          // A comment goes until the end of the line.
+          while (peek() != '\n' && !isAtEnd()) advance();
+        } else {
+          return;
+        }
+        break;
+      default:
+        return;
+    }
+  }
+}
+
+static bool isDigit(char c) {
+  return c >= '0' && c <= '9';
+}
+
+static bool isAlpha(char c) {
+  return (c >= 'a' && c <= 'z') ||
+         (c >= 'A' && c <= 'Z') ||
+          c == '_';
+}
+
+static Token number() {
+  while (isDigit(peek())) advance();
+
+  // Look for a fractional part.
+  if (peek() == '.' && isDigit(peekNext())) {
+    // Consume the ".".
+    advance();
+
+    while (isDigit(peek())) advance();
+  }
+
+  return newToken(TOKEN_NUMBER);
+}
+
+static Token string() {
+  while (peek() != '"' && !isAtEnd()) {
+    if (peek() == '\n') scanner.line++;
+    advance();
+  }
+
+  if (isAtEnd()) return errorToken("Unterminated string.");
+
+  // The closing quote.
+  advance();
+  return newToken(TOKEN_STRING);
+}
+
+static TokenType checkKeyword(int start, int length, const char *rest,
+                              TokenType type) {
+  if (scanner.current - scanner.start == start + length &&
+      memcmp(scanner.start + start, rest, length) == 0) {
+    return type;
+  }
+
+  return TOKEN_IDENTIFIER;
+}
+
+static TokenType identifierType() {
+  switch (scanner.start[0]) {
+  case 'a':
+    return checkKeyword(1, 2, "nd", TOKEN_AND);
+  case 'e':
+    return checkKeyword(1, 3, "lse", TOKEN_ELSE);
+  case 'f':
+    if (scanner.current - scanner.start > 1) {
+      switch (scanner.start[1]) {
+      case 'a':
+        return checkKeyword(2, 3, "lse", TOKEN_FALSE);
+      case 'o':
+        return checkKeyword(2, 1, "r", TOKEN_FOR);
+      }
+      return checkKeyword(1, 1, "n", TOKEN_FN);
+    }
+    break;
+  case 'i':
+    return checkKeyword(1, 1, "f", TOKEN_IF);
+  case 'n':
+    return checkKeyword(1, 2, "il", TOKEN_NIL);
+  case 'o':
+    return checkKeyword(1, 1, "r", TOKEN_OR);
+  case 'p':
+    return checkKeyword(1, 4, "rint", TOKEN_PRINT);
+  case 'r':
+    return checkKeyword(1, 5, "eturn", TOKEN_RETURN);
+  case 's':
+    return checkKeyword(1, 4, "uper", TOKEN_SUPER);
+  case 't':
+    if (scanner.current - scanner.start > 1) {
+      switch (scanner.start[1]) {
+      case 'h':
+        return checkKeyword(2, 2, "is", TOKEN_THIS);
+      case 'r':
+        return checkKeyword(2, 2, "ue", TOKEN_TRUE);
+      case 'y':
+        return checkKeyword(2, 2, "pe", TOKEN_TYPE);
+      }
+    }
+    break;
+  case 'l':
+    return checkKeyword(1, 2, "et", TOKEN_LET);
+  case 'w':
+    return checkKeyword(1, 4, "hile", TOKEN_WHILE);
+  }
+  return TOKEN_IDENTIFIER;
+}
+
+static Token identifier() {
+  while (isAlpha(peek()) || isDigit(peek())) advance();
+  return newToken(identifierType());
+}
+
+Token scanToken() {
+  skipWhitespace();
+  scanner.start = scanner.current;
+
+  if (isAtEnd()) return newToken(TOKEN_EOF);
+
+  char c = advance();
+  if (isAlpha(c)) return identifier();
+  if (isDigit(c)) return number();
+
+  switch (c) {
+    case '(': return newToken(TOKEN_LEFT_PAREN);
+    case ')': return newToken(TOKEN_RIGHT_PAREN);
+    case '{': return newToken(TOKEN_LEFT_BRACE);
+    case '}': return newToken(TOKEN_RIGHT_BRACE);
+    case '[': return newToken(TOKEN_LEFT_BRACKET);
+    case ']': return newToken(TOKEN_RIGHT_BRACKET);
+    case ';': return newToken(TOKEN_SEMICOLON);
+    case ':': return newToken(TOKEN_COLON);
+    case '#': return newToken(TOKEN_MESH);
+    case '$': return newToken(TOKEN_DOLLAR);
+    case '%': return newToken(TOKEN_PERCENT);
+    case '&': return newToken(TOKEN_AMPERSAND);
+    case '@': return newToken(TOKEN_AT);
+    case ',': return newToken(TOKEN_COMMA);
+    case '.': return newToken(TOKEN_DOT);
+    case '-': return newToken(TOKEN_MINUS);
+    case '+': return newToken(TOKEN_PLUS);
+    case '/': return newToken(TOKEN_SLASH);
+    case '*': return newToken(TOKEN_STAR);
+    case '!':
+      return newToken(
+          match('=') ? TOKEN_BANG_EQUAL : TOKEN_BANG);
+    case '=':
+      return newToken(
+          match('=') ? TOKEN_EQUAL_EQUAL : TOKEN_EQUAL);
+    case '<':
+      return newToken(
+          match('=') ? TOKEN_LESS_EQUAL : TOKEN_LESS);
+    case '>':
+      return newToken(
+          match('=') ? TOKEN_GREATER_EQUAL : TOKEN_GREATER);
+
+    case '"': return string();
+  }
+
+  return errorToken("Unexpected character.");
+}
+
diff --git a/src/scanner.h b/src/scanner.h
new file mode 100644
index 0000000..70c9f4f
--- /dev/null
+++ b/src/scanner.h
@@ -0,0 +1,70 @@
+#ifndef ztl_scanner_h
+#define ztl_scanner_h
+
+typedef enum {
+  // End of file
+  TOKEN_EOF,
+  // Single-character tokens.
+  TOKEN_LEFT_PAREN,
+  TOKEN_RIGHT_PAREN,
+  TOKEN_LEFT_BRACE,
+  TOKEN_RIGHT_BRACE,
+  TOKEN_LEFT_BRACKET,
+  TOKEN_RIGHT_BRACKET,
+  TOKEN_COMMA,
+  TOKEN_DOT,
+  TOKEN_MINUS,
+  TOKEN_PLUS,
+  TOKEN_COLON,
+  TOKEN_SEMICOLON,
+  TOKEN_SLASH,
+  TOKEN_STAR,
+  TOKEN_MESH,
+  TOKEN_DOLLAR,
+  TOKEN_AT,
+  TOKEN_AMPERSAND,
+  TOKEN_PERCENT,
+  // One or two character tokens.
+  TOKEN_BANG,
+  TOKEN_BANG_EQUAL,
+  TOKEN_EQUAL,
+  TOKEN_EQUAL_EQUAL,
+  TOKEN_GREATER,
+  TOKEN_GREATER_EQUAL,
+  TOKEN_LESS,
+  TOKEN_LESS_EQUAL,
+  // Literals.
+  TOKEN_IDENTIFIER,
+  TOKEN_STRING,
+  TOKEN_NUMBER,
+  // Keywords.
+  TOKEN_AND,
+  TOKEN_TYPE,
+  TOKEN_ELSE,
+  TOKEN_FALSE,
+  TOKEN_FOR,
+  TOKEN_FN,
+  TOKEN_IF,
+  TOKEN_NIL,
+  TOKEN_OR,
+  TOKEN_PRINT,
+  TOKEN_RETURN,
+  TOKEN_SUPER,
+  TOKEN_THIS,
+  TOKEN_TRUE,
+  TOKEN_LET,
+  TOKEN_WHILE,
+  TOKEN_ERROR,
+} TokenType;
+
+typedef struct {
+  TokenType type;
+  const char *start;
+  int length;
+  int line;
+} Token;
+
+void newScanner(const char *source);
+Token scanToken();
+
+#endif
diff --git a/src/vm.c b/src/vm.c
index 715446c..bd909b9 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1,4 +1,5 @@
 #include "common.h"
+#include "compiler.h"
 #include "debug.h"
 #include "vm.h"
 
@@ -76,9 +77,22 @@ static InterpretResult run() {
 #undef BINARY_OP
 }
 
-InterpretResult interpret(Chunk* chunk) {
-  vm.chunk = chunk;
+InterpretResult interpret(const char* source) {
+  Chunk chunk;
+  newChunk(&chunk);
+
+  if (!compile(source, &chunk)) {
+    freeChunk(&chunk);
+    return INTERPRET_COMPILE_ERROR;
+  }
+
+  vm.chunk = &chunk;
   vm.ip = vm.chunk->code;
-  return run();
+
+  InterpretResult result = run();
+
+  freeChunk(&chunk);
+  return result;
 }
 
+
diff --git a/src/vm.h b/src/vm.h
index aeec3f2..50cd09b 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -21,7 +21,7 @@ typedef enum {
 
 void newVM();
 void freeVM();
-InterpretResult interpret(Chunk *chunk);
+InterpretResult interpret(const char* source);
 void push(Value value);
 Value pop();