diff --git a/furvm/include/furvm/constant.hpp b/furvm/include/furvm/constant.hpp
new file mode 100644
index 0000000..419aba5
--- /dev/null
+++ b/furvm/include/furvm/constant.hpp
@@ -0,0 +1,112 @@
+#ifndef FURVM_CONSTANT_HPP
+#define FURVM_CONSTANT_HPP
+
+#include "furvm/fwd.hpp"
+
+#include <exception>
+#include <string_view>
+
+namespace furvm {
+
+/**
+ * @brief Bad constant access exception.
+ */
+class bad_constant_access : public std::exception {
+public:
+    bad_constant_access()           = default;
+    ~bad_constant_access() override = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    bad_constant_access(bad_constant_access&&) noexcept = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    bad_constant_access& operator=(bad_constant_access&&) noexcept = default;
+
+    /**
+     * @brief Copy constructor.
+     */
+    bad_constant_access(const bad_constant_access&) = default;
+
+    /**
+     * @brief Copy constructor.
+     */
+    bad_constant_access& operator=(const bad_constant_access&) = default;
+public:
+    /**
+     * @brief Returns a C-style string describing the cause of the error.
+     *
+     * @return The cause of the error.
+     */
+    const char* what() const noexcept override { return "bad constant access"; }
+};
+
+enum class constant_t : std::uint8_t {
+    String, /**< String constant. */
+};
+
+class constant {
+public:
+    using string_type = std::string_view; /**< String constant type. */
+public:
+    /**
+     * @brief Construct a new string constant.
+     *
+     * @param string String.
+     */
+    constant(string_type string)
+      : m_type(constant_t::String), m_value(string) {}
+
+    ~constant() = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    constant(constant&&) = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    constant& operator=(constant&&) = default;
+
+    constant(const constant&)            = delete;
+    constant& operator=(const constant&) = delete;
+public:
+    /**
+     * @brief Returns this constant's type.
+     * @see constant_t
+     *
+     * @return The constant type.
+     */
+    constexpr constant_t type() const { return m_type; }
+
+    /**
+     * @brief Returns this constant's string value.
+     * @throws bad_constant_access if this constant's type is not constant_t::String.
+     *
+     * @return The string value.
+     */
+    constexpr string_type string() const {
+        require_type(constant_t::String);
+        return m_value.string;
+    }
+private:
+    void require_type(constant_t type) const {
+        if (m_type != type) throw bad_constant_access();
+    }
+private:
+    constant_t m_type{};
+    union value {
+        string_type string;
+
+        value(string_type sv)
+          : string(sv) {}
+    } m_value;
+};
+
+} // namespace furvm
+
+#endif // FURVM_CONSTANT_HPP
\ No newline at end of file
diff --git a/furvm/include/furvm/context.hpp b/furvm/include/furvm/context.hpp
index 499c1f4..496ab47 100644
--- a/furvm/include/furvm/context.hpp
+++ b/furvm/include/furvm/context.hpp
@@ -1,14 +1,18 @@
 #ifndef FURVM_CONTEXT_HPP
 #define FURVM_CONTEXT_HPP
 
+#include "furvm/fwd.hpp"
+#include "furvm/module.hpp"
+
+#include <memory>
+#include <type_traits>
+#include <vector>
+
 namespace furvm {
 
-/**
- * @brief Context.
- *
- * A furvm context.
- */
 class context {
+public:
+    using value_type = std::unique_ptr<mod>;
 public:
     context()  = default;
     ~context() = default;
@@ -25,7 +29,71 @@ public:
 
     context(const context&)            = delete;
     context& operator=(const context&) = delete;
+public:
+    /**
+     * @brief Adds a module to this context.
+     *
+     * @param args Arguments to forward to module's constructor.
+     * @return An index to the emplaced module.
+     */
+    template <typename... Args, typename = std::enable_if_t<std::is_constructible_v<mod, Args...>>>
+    constexpr module_index emplace(Args&&... args) {
+        module_index index = m_modules.size();
+        m_modules.emplace_back(std::make_unique<mod>(std::forward<Args>(args)...));
+        return index;
+    }
+
+    /**
+     * @brief Erases a module from this context.
+     *
+     * @param index Index to the module.
+     * @return Old value.
+     */
+    value_type erase(module_index index) {
+        if (index >= m_modules.size()) return nullptr;
+        return std::move(m_modules[index]);
+    }
+
+    /**
+     * @brief Returns a module of this context.
+     *
+     * @param index Position of the module.
+     * @return The module.
+     */
+    constexpr value_type& operator[](module_index index) { return m_modules[index]; }
+
+    /**
+     * @brief Returns a module of this context.
+     *
+     * @param index Position of the module.
+     * @return The module.
+     */
+    constexpr const value_type& operator[](module_index index) const { return m_modules[index]; }
+
+    /**
+     * @brief Returns a module of this context.
+     *
+     * @param index Position of the module.
+     * @return The module.
+     */
+    constexpr value_type& at(module_index index) { return m_modules.at(index); }
+
+    /**
+     * @brief Returns a module of this context.
+     *
+     * @param index Position of the module.
+     * @return The module.
+     */
+    constexpr const value_type& at(module_index index) const { return m_modules.at(index); }
+
+    /**
+     * @brief Returns how many does this context have modules.
+     *
+     * @return The module count.
+     */
+    constexpr size_t size() const { return m_modules.size(); }
 private:
+    std::vector<std::unique_ptr<mod>> m_modules;
 };
 
 } // namespace furvm
diff --git a/furvm/include/furvm/fwd.hpp b/furvm/include/furvm/fwd.hpp
new file mode 100644
index 0000000..5b1a9ee
--- /dev/null
+++ b/furvm/include/furvm/fwd.hpp
@@ -0,0 +1,74 @@
+#ifndef FURVM_FWD_HPP
+#define FURVM_FWD_HPP
+
+#include <cstddef> // IWYU pragma: export
+#include <cstdint> // IWYU pragma: export
+
+/**
+ * @brief Furlang's virtual machine.
+ */
+namespace furvm {
+
+// constant.hpp
+
+/**
+ * @brief Constant index.
+ *
+ * An index to the constant in module's constant pool.
+ */
+using constant_index = std::uint16_t;
+
+/**
+ * @enum constant_t
+ * @brief Constant type.
+ */
+enum class constant_t : std::uint8_t;
+
+/**
+ * @class constant
+ * @brief Constant.
+ */
+class constant;
+
+// instruction.hpp
+
+/**
+ * @enum instruction_t
+ * @brief Furvm's instruction type.
+ */
+enum class instruction_t : std::uint8_t;
+
+/**
+ * @struct instruction
+ * @brief Furvm's instruction.
+ */
+struct instruction;
+
+// module.hpp
+
+/**
+ * @class mod
+ * @brief Module.
+ *
+ * A furvm module. Translation unit of furlang.
+ */
+class mod;
+
+/**
+ * @brief Furvm module's index.
+ */
+using module_index = std::size_t;
+
+// context.hpp
+
+/**
+ * @class context
+ * @brief Context.
+ *
+ * A furvm context.
+ */
+class context;
+
+} // namespace furvm
+
+#endif // FURVM_FWD_HPP
\ No newline at end of file
diff --git a/furvm/include/furvm/instruction.hpp b/furvm/include/furvm/instruction.hpp
new file mode 100644
index 0000000..1e6b4f5
--- /dev/null
+++ b/furvm/include/furvm/instruction.hpp
@@ -0,0 +1,45 @@
+#ifndef FURVM_INSTRUCTION_HPP
+#define FURVM_INSTRUCTION_HPP
+
+#include "furvm/fwd.hpp"
+
+namespace furvm {
+
+enum class instruction_t : std::uint8_t {
+    /**
+     * @brief No operation.
+     */
+    NoOperation = 0,
+
+    /**
+     * @brief Pushes a constant onto the stack.
+     *
+     * Pushes a constant from the constant pool denoted by two next bytes in low-endian onto the stack.
+     */
+    PushConstant,
+
+    /**
+     * @brief Pops top element from the stack.
+     */
+    Drop,
+
+    /**
+     * @brief Duplicates top element on the stack.
+     */
+    Duplicate,
+};
+
+struct instruction {
+    instruction_t type; /**< Instruction type. */
+
+    /**
+     * @brief Instruction value.
+     */
+    union value {
+        constant_index constant; /**< Constant instruction argument. */
+    } value;                     /**< Instruction value. */
+};
+
+} // namespace furvm
+
+#endif // FURVM_INSTRUCTION_HPP
\ No newline at end of file
diff --git a/furvm/include/furvm/module.hpp b/furvm/include/furvm/module.hpp
new file mode 100644
index 0000000..5c67b30
--- /dev/null
+++ b/furvm/include/furvm/module.hpp
@@ -0,0 +1,28 @@
+#ifndef FURVM_MODULE_HPP
+#define FURVM_MODULE_HPP
+
+namespace furvm {
+
+class mod {
+public:
+    mod()  = default;
+    ~mod() = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    mod(mod&&) = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    mod& operator=(mod&&) = default;
+
+    mod(const mod&)            = delete;
+    mod& operator=(const mod&) = delete;
+private:
+};
+
+} // namespace furvm
+
+#endif // FURVM_MODULE_HPP
\ No newline at end of file
diff --git a/furvm/src/main.cpp b/furvm/src/main.cpp
index 001cc5f..6b537b2 100644
--- a/furvm/src/main.cpp
+++ b/furvm/src/main.cpp
@@ -5,6 +5,8 @@
 int main(void) {
     furvm::context context;
 
+    auto mainModule = context.emplace();
+
     return 0;
 }
 
diff --git a/furvm/src/module.cpp b/furvm/src/module.cpp
new file mode 100644
index 0000000..ce10db3
--- /dev/null
+++ b/furvm/src/module.cpp
@@ -0,0 +1,3 @@
+#include "furvm/module.hpp"
+
+namespace furvm {}
\ No newline at end of file