diff --git a/src/builtin.c b/src/builtin.c
index 0d3a7b7..c243602 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -46,3 +46,51 @@ AST* builtin_sub(size_t argc, AST** argv) {
 
     return ast_init(AST_TYPE_NUM, ast_num_data_init(total));
 }
+
+AST* builtin_mul(size_t argc, AST** argv) {
+    log_dbg("Got here");
+    AST* first = exec_exp(*argv);
+    if (first->type != AST_TYPE_NUM)
+        return ast_init(
+            AST_TYPE_EXC, ast_exc_data_init("Can't multiply non-num arguments.")
+        );
+
+    ASTNumData total = *(ASTNumData*)first->data;
+
+    for (int i = 1; i < argc; i++) {
+        AST* arg = exec_exp(argv[i]);
+        if (arg->type != AST_TYPE_NUM)
+            return ast_init(
+                AST_TYPE_EXC,
+                ast_exc_data_init("Can't multiply non-num arguments.")
+            );
+
+        total *= *(ASTNumData*)arg->data;
+    }
+
+    return ast_init(AST_TYPE_NUM, ast_num_data_init(total));
+}
+
+AST* builtin_div(size_t argc, AST** argv) {
+    log_dbg("Got here");
+    AST* first = exec_exp(*argv);
+    if (first->type != AST_TYPE_NUM)
+        return ast_init(
+            AST_TYPE_EXC, ast_exc_data_init("Can't divide non-num arguments.")
+        );
+
+    ASTNumData total = *(ASTNumData*)first->data;
+
+    for (int i = 1; i < argc; i++) {
+        AST* arg = exec_exp(argv[i]);
+        if (arg->type != AST_TYPE_NUM)
+            return ast_init(
+                AST_TYPE_EXC,
+                ast_exc_data_init("Can't divide non-num arguments.")
+            );
+
+        total /= *(ASTNumData*)arg->data;
+    }
+
+    return ast_init(AST_TYPE_NUM, ast_num_data_init(total));
+}
diff --git a/src/exec.c b/src/exec.c
index 58ccee7..ce3604f 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -26,6 +26,14 @@ AST* exec_start(AST* ast) {
         global, "sub", ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_sub))
     );
 
+    htab_ins(
+        global, "mul", ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_mul))
+    );
+
+    htab_ins(
+        global, "div", ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_div))
+    );
+
     // Push global namespace to `scope`.
     stack_push(scope, global);
 
diff --git a/src/include/builtin.h b/src/include/builtin.h
index 7e37c4f..c4c58f3 100644
--- a/src/include/builtin.h
+++ b/src/include/builtin.h
@@ -9,9 +9,15 @@ AST* builtin_sum(size_t argc, AST** argv);
 // Subtract nums.
 AST* builtin_sub(size_t argc, AST** argv);
 
+// Multiply nums.
+AST* builtin_mul(size_t argc, AST** argv);
+
+// Divide nums.
+AST* builtin_div(size_t argc, AST** argv);
+
 // The list of built-in functions.
 static AST* (*builtin_fns[])(size_t argc, AST** argv) = {
-    builtin_sum, builtin_sub
+    builtin_sum, builtin_sub, builtin_mul, builtin_div
 };
 
 #endif