diff --git a/doc/grammar.bnf b/doc/grammar.bnf
index 044280f..cb7e123 100644
--- a/doc/grammar.bnf
+++ b/doc/grammar.bnf
@@ -1,6 +1,7 @@
 MODULE ::= EXPR*
 EXPR ::=
   bool
+| int
 | ident
 | VARDECL
 | FUNCALL
diff --git a/examples/int.gri b/examples/int.gri
new file mode 100644
index 0000000..521c083
--- /dev/null
+++ b/examples/int.gri
@@ -0,0 +1,28 @@
+(assert-eq? 7 7)
+
+(assert-eq? 0 (+))
+(assert-eq? 3 (+ 3))
+(assert-eq? 5 (+ 2 3))
+
+(assert-eq? 0 (-))
+(assert-eq? -3 (- 3))
+(assert-eq? -1 (- 2 3))
+(assert-eq? 5 (- 8 3))
+
+(assert-eq? 1 (*))
+(assert-eq? 6 (* 3 2))
+(assert-eq? 120 (* 1 2 3 4 5))
+
+(assert-eq? 1 (/))
+(assert-eq? 6 (/ 6))
+(assert-eq? 3 (/ 6 2))
+(assert-eq? 2 (/ 12 2 3))
+
+(assert-eq? 1 (%))
+(assert-eq? 3 (% 7 4))
+(assert-eq? 2 (% 13 7 4))
+
+(assert-eq? 1 (^))
+(assert-eq? 2 (^ 2))
+(assert-eq? 8 (^ 2 3))
+(assert-eq? 64 (^ 2 3 2))
diff --git a/lib/core.cpp b/lib/core.cpp
index 632ba61..bc16b21 100644
--- a/lib/core.cpp
+++ b/lib/core.cpp
@@ -3,9 +3,156 @@
 
 GRINO_ERROR(assertion_error);
 
+extern "C" void lib_int(grino::Loader& loader)
+{
+  loader.add_native("+", [](auto args){
+    int result = 0;
+
+    for (auto value: args)
+      {
+        result += value->as_int();
+      }
+
+    grino::Loc loc {"???", 0};
+
+    if (args.empty() == false)
+      {
+        loc = args.front()->loc();
+      }
+
+    return grino::Value::make_int(loc, result);
+  });
+
+  loader.add_native("*", [](auto args){
+    int result = 1;
+
+    for (auto value: args)
+      {
+        result *= value->as_int();
+      }
+
+    grino::Loc loc {"???", 0};
+
+    if (args.empty() == false)
+      {
+        loc = args.front()->loc();
+      }
+
+    return grino::Value::make_int(loc, result);
+  });
+
+  loader.add_native("-", [](auto args){
+    grino::Loc loc {"???", 0};
+
+    if (args.empty() == false)
+      {
+        loc = args.front()->loc();
+      }
+    else
+      {
+        return grino::Value::make_int(loc, 0);
+      }
+
+    int result = args[0]->as_int();
+
+    if (args.size() == 1)
+      {
+        return grino::Value::make_int(loc, -result);
+      }
+
+    for (size_t i=1; i<args.size(); i++)
+      {
+        result -= args[i]->as_int();
+      }
+
+    return grino::Value::make_int(loc, result);
+  });
+
+  loader.add_native("/", [](auto args){
+    grino::Loc loc {"???", 0};
+
+    if (args.empty() == false)
+      {
+        loc = args.front()->loc();
+      }
+    else
+      {
+        return grino::Value::make_int(loc, 1);
+      }
+
+    int result = args[0]->as_int();
+
+    if (args.size() == 1)
+      {
+        return grino::Value::make_int(loc, result);
+      }
+
+    for (size_t i=1; i<args.size(); i++)
+      {
+        result /= args[i]->as_int();
+      }
+
+    return grino::Value::make_int(loc, result);
+  });
+
+  loader.add_native("%", [](auto args){
+    grino::Loc loc {"???", 0};
+
+    if (args.empty() == false)
+      {
+        loc = args.front()->loc();
+      }
+    else
+      {
+        return grino::Value::make_int(loc, 1);
+      }
+
+    int result = args[0]->as_int();
+
+    if (args.size() == 1)
+      {
+        return grino::Value::make_int(loc, result);
+      }
+
+    for (size_t i=1; i<args.size(); i++)
+      {
+        result %= args[i]->as_int();
+      }
+
+    return grino::Value::make_int(loc, result);
+  });
+
+  loader.add_native("^", [](auto args){
+    grino::Loc loc {"???", 0};
+
+    if (args.empty() == false)
+      {
+        loc = args.front()->loc();
+      }
+    else
+      {
+        return grino::Value::make_int(loc, 1);
+      }
+
+    int result = args[0]->as_int();
+
+    if (args.size() == 1)
+      {
+        return grino::Value::make_int(loc, result);
+      }
+
+    for (size_t i=1; i<args.size(); i++)
+      {
+        result = std::pow(result, args[i]->as_int());
+      }
+
+    return grino::Value::make_int(loc, result);
+  });
+}
+
 extern "C" void lib_assert(grino::Loader& loader)
 {
-    loader.add_native("assert", [](auto args){
+  loader.add_native("assert", [](auto args){
 
     for (auto value: args)
       {
@@ -21,7 +168,7 @@ extern "C" void lib_assert(grino::Loader& loader)
     return grino::Value::make_bool(args.front()->loc(), true);
   });
 
-      loader.add_native("assert-eq?", [](auto args){
+  loader.add_native("assert-eq?", [](auto args){
     auto lhs = args.front();
 
     for (size_t i=1; i<args.size(); i++)
@@ -50,6 +197,7 @@ extern "C" void lib_assert(grino::Loader& loader)
 extern "C" void lib(grino::Loader& loader)
 {
   lib_assert(loader);
+  lib_int(loader);
 
   loader.add_native("dump", [](auto args){
     std::string sep;
diff --git a/src/Compiler.cpp b/src/Compiler.cpp
index 58cf75b..7277667 100644
--- a/src/Compiler.cpp
+++ b/src/Compiler.cpp
@@ -46,6 +46,14 @@ namespace grino
                            program.push_constant(value));
       } break;
 
+      case NODE_INT: {
+        std::string repr = node->repr();
+        auto value = Value::make_int(node->loc(), std::stoi(repr));
+
+        program.push_instr(OPCODE_LOAD_CONST,
+                           program.push_constant(value));
+      } break;
+
       case NODE_VARDECL: {
         std::string ident = node->child(0).lock()->repr();
         auto expr = node->child(1).lock();
diff --git a/src/Lexer.cpp b/src/Lexer.cpp
index f028f40..3db6e15 100644
--- a/src/Lexer.cpp
+++ b/src/Lexer.cpp
@@ -14,6 +14,7 @@ namespace grino
     add_keyword(NODE_BOOL, "true", true);
     add_keyword(NODE_BOOL, "false", true);
 
+    m_scanners.push_back(std::bind(&Lexer::scan_int, this));
     m_scanners.push_back(std::bind(&Lexer::scan_ident, this));
   }
 
@@ -222,4 +223,35 @@ namespace grino
 
     return std::nullopt;
   }
+
+  std::optional<ScanInfo> Lexer::scan_int()
+  {
+    size_t cursor = m_cursor;
+    std::string repr;
+
+    if (has_more(cursor) && at(cursor) == '-')
+      {
+        repr += "-";
+        cursor++;
+      }
+
+    while (has_more(cursor)
+           && std::isdigit(at(cursor)))
+      {
+        repr += at(cursor);
+        cursor++;
+      }
+
+    if (repr.empty()
+        || repr.back() == '-')
+      {
+        return std::nullopt;
+      }
+
+    return ScanInfo {
+      cursor,
+      NODE_INT,
+      repr
+    };
+  }
 }
diff --git a/src/Lexer.hpp b/src/Lexer.hpp
index 5f82807..6ccebeb 100644
--- a/src/Lexer.hpp
+++ b/src/Lexer.hpp
@@ -58,6 +58,7 @@ namespace grino
                                          bool has_value);
 
     std::optional<ScanInfo> scan_ident();
+    std::optional<ScanInfo> scan_int();
   };
 }
 
diff --git a/src/Node.hpp b/src/Node.hpp
index 30d2bfa..513bfc3 100644
--- a/src/Node.hpp
+++ b/src/Node.hpp
@@ -7,6 +7,7 @@
 #define NODE_TYPE(G)                            \
   G(NODE_MODULE),                               \
     G(NODE_BOOL),                               \
+    G(NODE_INT),                                \
     G(NODE_VARDECL),                            \
     G(NODE_FUNCALL),                            \
     G(NODE_IDENT),                              \
diff --git a/src/Parser.cpp b/src/Parser.cpp
index d088c99..7728655 100644
--- a/src/Parser.cpp
+++ b/src/Parser.cpp
@@ -128,7 +128,8 @@ namespace grino
       }
 
     if (type_is(NODE_IDENT)
-        || type_is(NODE_BOOL))
+        || type_is(NODE_BOOL)
+        || type_is(NODE_INT))
       {
         return consume();
       }
diff --git a/src/Value.cpp b/src/Value.cpp
index 9259bdc..55e0c6e 100644
--- a/src/Value.cpp
+++ b/src/Value.cpp
@@ -17,6 +17,14 @@ namespace grino
     return value;
   }
 
+  /*static*/ std::shared_ptr<Value> Value::make_int(Loc const& loc, int val)
+  {
+    auto value = std::make_shared<Value>(loc);
+    value->m_type = TYPE_INT;
+    value->m_int_val = val;
+    return value;
+  }
+
   /*static*/
   std::shared_ptr<Value> Value::make_native_function(Loc const& loc,
                                                      native_t val)
@@ -40,6 +48,7 @@ namespace grino
     switch (m_type)
       {
       case TYPE_NIL: return "<nil>";
+      case TYPE_INT: return std::to_string(*m_int_val);
       case TYPE_BOOL: return *m_bool_val ? "true" : "false";
       case TYPE_FUNCTION: return "<function>";
       case TYPE_REF: return "&" + std::to_string(*m_ref_val);
@@ -58,6 +67,7 @@ namespace grino
       {
       case TYPE_NIL: return true;
       case TYPE_BOOL: return *m_bool_val == *other.m_bool_val;
+      case TYPE_INT: return *m_int_val == *other.m_int_val;
       case TYPE_REF: return *m_ref_val == *other.m_ref_val;
 
       default:
diff --git a/src/Value.hpp b/src/Value.hpp
index 7b212a7..6d5f8bd 100644
--- a/src/Value.hpp
+++ b/src/Value.hpp
@@ -13,6 +13,7 @@ namespace grino
   public:
     static std::shared_ptr<Value> make_nil(Loc const& loc);
     static std::shared_ptr<Value> make_bool(Loc const& loc, bool val);
+    static std::shared_ptr<Value> make_int(Loc const& loc, int val);
     static std::shared_ptr<Value> make_native_function(Loc const& loc,
                                                        native_t val);
     static std::shared_ptr<Value> make_ref(Loc const& loc,
@@ -24,6 +25,7 @@ namespace grino
     Loc loc() const { return m_loc; }
     TypeType type() const { return m_type; }
     bool as_bool() const { return *m_bool_val; }
+    int as_int() const { return *m_int_val; }
     std::shared_ptr<Function> as_function() const { return m_function_val; }
     size_t as_ref() const { return *m_ref_val; }
 
@@ -34,6 +36,7 @@ namespace grino
     Loc m_loc;
     TypeType m_type = TYPE_NIL;
     std::optional<bool> m_bool_val;
+    std::optional<int> m_int_val;
     std::shared_ptr<Function> m_function_val;
     std::optional<size_t> m_ref_val;
   };
diff --git a/src/commons.hpp b/src/commons.hpp
index 36354ec..403478b 100644
--- a/src/commons.hpp
+++ b/src/commons.hpp
@@ -2,6 +2,7 @@
 #define grino_COMMONS_HPP
 
 #include <cassert>
+#include <cmath>
 #include <fstream>
 #include <iostream>
 #include <filesystem>
diff --git a/src/types.hpp b/src/types.hpp
index d989f6d..8a0cf5f 100644
--- a/src/types.hpp
+++ b/src/types.hpp
@@ -6,6 +6,7 @@
 #define TYPES(G)                                \
   G(TYPE_NIL),                                  \
     G(TYPE_BOOL),                               \
+    G(TYPE_INT),                                \
     G(TYPE_FUNCTION),                           \
     G(TYPE_REF)
 
diff --git a/tests/Lexer.cpp b/tests/Lexer.cpp
index 642f3c0..ccab9c0 100644
--- a/tests/Lexer.cpp
+++ b/tests/Lexer.cpp
@@ -77,3 +77,16 @@ TEST_CASE_METHOD(LexerTest, "Lexer_no_end_space")
   test_next(lexer, "CPAR");
   test_end(lexer);
 }
+
+TEST_CASE_METHOD(LexerTest, "Lexer_int")
+{
+  grino::Lexer lexer {m_logger, "tests/lexer"};
+
+  lexer.scan("4 39 256 2 -7");
+  test_next(lexer, "INT[4]");
+  test_next(lexer, "INT[39]");
+  test_next(lexer, "INT[256]");
+  test_next(lexer, "INT[2]");
+  test_next(lexer, "INT[-7]");
+  test_end(lexer);
+}
diff --git a/tests/Parser.cpp b/tests/Parser.cpp
index 72ac39e..f01921c 100644
--- a/tests/Parser.cpp
+++ b/tests/Parser.cpp
@@ -48,3 +48,9 @@ TEST_CASE_METHOD(ParserTest, "Parser_funcall")
   test_parse("MODULE(FUNCALL(IDENT[f],BOOL[false],BOOL[true]))",
              "(f false true)");
 }
+
+TEST_CASE_METHOD(ParserTest, "Parser_integer")
+{
+  test_parse("MODULE(FUNCALL(IDENT[hello],INT[2],INT[34]))",
+             "(hello 2 34)");
+}