diff --git a/chibicc.h b/chibicc.h
index 3d59afb..4c8a222 100644
--- a/chibicc.h
+++ b/chibicc.h
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <ctype.h>
 #include <stdarg.h>
@@ -6,10 +7,13 @@
 #include <stdlib.h>
 #include <string.h>
 
+typedef struct Node Node;
+
 //
 // tokenize.c
 //
 
+// Token
 typedef enum {
   TK_IDENT, // Identifiers
   TK_PUNCT, // Punctuators
@@ -38,6 +42,23 @@ Token *tokenize(char *input);
 // parse.c
 //
 
+// Local variable
+typedef struct Obj Obj;
+struct Obj {
+  Obj *next;
+  char *name; // Variable name
+  int offset; // Offset from RBP
+};
+
+// Function
+typedef struct Function Function;
+struct Function {
+  Node *body;
+  Obj *locals;
+  int stack_size;
+};
+
+// AST node
 typedef enum {
   ND_ADD,       // +
   ND_SUB,       // -
@@ -55,20 +76,19 @@ typedef enum {
 } NodeKind;
 
 // AST node type
-typedef struct Node Node;
 struct Node {
   NodeKind kind; // Node kind
   Node *next;    // Next node
   Node *lhs;     // Left-hand side
   Node *rhs;     // Right-hand side
-  char name;     // Used if kind == ND_VAR
+  Obj *var;      // Used if kind == ND_VAR
   int val;       // Used if kind == ND_NUM
 };
 
-Node *parse(Token *tok);
+Function *parse(Token *tok);
 
 //
 // codegen.c
 //
 
-void codegen(Node *node);
+void codegen(Function *prog);
diff --git a/codegen.c b/codegen.c
index adc4924..8afaa47 100644
--- a/codegen.c
+++ b/codegen.c
@@ -12,12 +12,17 @@ static void pop(char *arg) {
   depth--;
 }
 
+// Round up `n` to the nearest multiple of `align`. For instance,
+// align_to(5, 8) returns 8 and align_to(11, 8) returns 16.
+static int align_to(int n, int align) {
+  return (n + align - 1) / align * align;
+}
+
 // Compute the absolute address of a given node.
 // It's an error if a given node does not reside in memory.
 static void gen_addr(Node *node) {
   if (node->kind == ND_VAR) {
-    int offset = (node->name - 'a' + 1) * 8;
-    printf("  lea %d(%%rbp), %%rax\n", -offset);
+    printf("  lea %d(%%rbp), %%rax\n", node->var->offset);
     return;
   }
 
@@ -97,16 +102,28 @@ static void gen_stmt(Node *node) {
   error("invalid statement");
 }
 
-void codegen(Node *node) {
+// Assign offsets to local variables.
+static void assign_lvar_offsets(Function *prog) {
+  int offset = 0;
+  for (Obj *var = prog->locals; var; var = var->next) {
+    offset += 8;
+    var->offset = -offset;
+  }
+  prog->stack_size = align_to(offset, 16);
+}
+
+void codegen(Function *prog) {
+  assign_lvar_offsets(prog);
+
   printf("  .globl main\n");
   printf("main:\n");
 
   // Prologue
   printf("  push %%rbp\n");
   printf("  mov %%rsp, %%rbp\n");
-  printf("  sub $208, %%rsp\n");
+  printf("  sub $%d, %%rsp\n", prog->stack_size);
 
-  for (Node *n = node; n; n = n->next) {
+  for (Node *n = prog->body; n; n = n->next) {
     gen_stmt(n);
     assert(depth == 0);
   }
diff --git a/main.c b/main.c
index adb525c..a855d90 100644
--- a/main.c
+++ b/main.c
@@ -5,7 +5,10 @@ int main(int argc, char **argv) {
     error("%s: invalid number of arguments", argv[0]);
 
   Token *tok = tokenize(argv[1]);
-  Node *node = parse(tok);
-  codegen(node);
+  Function *prog = parse(tok);
+
+  // Traverse the AST to emit assembly.
+  codegen(prog);
+
   return 0;
 }
diff --git a/parse.c b/parse.c
index f9b8e58..49c5646 100644
--- a/parse.c
+++ b/parse.c
@@ -1,5 +1,9 @@
 #include "chibicc.h"
 
+// All local variable instances created during parsing are
+// accumulated to this list.
+Obj *locals;
+
 static Node *expr(Token **rest, Token *tok);
 static Node *expr_stmt(Token **rest, Token *tok);
 static Node *assign(Token **rest, Token *tok);
@@ -10,6 +14,14 @@ static Node *mul(Token **rest, Token *tok);
 static Node *unary(Token **rest, Token *tok);
 static Node *primary(Token **rest, Token *tok);
 
+// Find a local variable by name.
+static Obj *find_var(Token *tok) {
+  for (Obj *var = locals; var; var = var->next)
+    if (strlen(var->name) == tok->len && !strncmp(tok->loc, var->name, tok->len))
+      return var;
+  return NULL;
+}
+
 static Node *new_node(NodeKind kind) {
   Node *node = calloc(1, sizeof(Node));
   node->kind = kind;
@@ -35,12 +47,20 @@ static Node *new_num(int val) {
   return node;
 }
 
-static Node *new_var_node(char name) {
+static Node *new_var_node(Obj *var) {
   Node *node = new_node(ND_VAR);
-  node->name = name;
+  node->var = var;
   return node;
 }
 
+static Obj *new_lvar(char *name) {
+  Obj *var = calloc(1, sizeof(Obj));
+  var->name = name;
+  var->next = locals;
+  locals = var;
+  return var;
+}
+
 // stmt = expr-stmt
 static Node *stmt(Token **rest, Token *tok) {
   return expr_stmt(rest, tok);
@@ -178,9 +198,11 @@ static Node *primary(Token **rest, Token *tok) {
   }
 
   if (tok->kind == TK_IDENT) {
-    Node *node = new_var_node(*tok->loc);
+    Obj *var = find_var(tok);
+    if (!var)
+      var = new_lvar(strndup(tok->loc, tok->len));
     *rest = tok->next;
-    return node;
+    return new_var_node(var);
   }
 
   if (tok->kind == TK_NUM) {
@@ -193,10 +215,15 @@ static Node *primary(Token **rest, Token *tok) {
 }
 
 // program = stmt*
-Node *parse(Token *tok) {
+Function *parse(Token *tok) {
   Node head = {};
   Node *cur = &head;
+
   while (tok->kind != TK_EOF)
     cur = cur->next = stmt(&tok, tok);
-  return head.next;
+
+  Function *prog = calloc(1, sizeof(Function));
+  prog->body = head.next;
+  prog->locals = locals;
+  return prog;
 }
diff --git a/test.sh b/test.sh
index fb6888a..e813368 100755
--- a/test.sh
+++ b/test.sh
@@ -46,10 +46,13 @@ assert 1 '1>=0;'
 assert 1 '1>=1;'
 assert 0 '1>=2;'
 
-assert 3 '1; 2; 3;'
+assert 3 'a=3; a;'
+assert 8 'a=3; z=5; a+z;'
 
 assert 3 'a=3; a;'
 assert 8 'a=3; z=5; a+z;'
 assert 6 'a=b=3; a+b;'
+assert 3 'foo=3; foo;'
+assert 8 'foo123=3; bar=5; foo123+bar;'
 
 echo OK
diff --git a/tokenize.c b/tokenize.c
index dfecaf6..e89d569 100644
--- a/tokenize.c
+++ b/tokenize.c
@@ -60,6 +60,16 @@ static bool startswith(char *p, char *q) {
   return strncmp(p, q, strlen(q)) == 0;
 }
 
+// Returns true if c is valid as the first character of an identifier.
+static bool is_ident1(char c) {
+  return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_';
+}
+
+// Returns true if c is valid as a non-first character of an identifier.
+static bool is_ident2(char c) {
+  return is_ident1(c) || ('0' <= c && c <= '9');
+}
+
 // Read a punctuator token from p and returns its length.
 static int read_punct(char *p) {
   if (startswith(p, "==") || startswith(p, "!=") ||
@@ -92,9 +102,12 @@ Token *tokenize(char *p) {
     }
 
     // Identifier
-    if ('a' <= *p && *p <= 'z') {
-      cur = cur->next = new_token(TK_IDENT, p, p + 1);
-      p++;
+    if (is_ident1(*p)) {
+      char *start = p;
+      do {
+        p++;
+      } while (is_ident2(*p));
+      cur = cur->next = new_token(TK_IDENT, start, p);
       continue;
     }