diff --git a/include/wrenpp/StringCRC32.hpp b/include/wrenpp/StringCRC32.hpp
new file mode 100644
index 0000000..6c3ac8c
--- /dev/null
+++ b/include/wrenpp/StringCRC32.hpp
@@ -0,0 +1,148 @@
+#ifndef id42C91D2875AE4E56BA61051619B58C03
+#define id42C91D2875AE4E56BA61051619B58C03
+
+#include <cstdint>
+#include <cstddef>
+
+namespace duckcore {
+	class StringCRC32 {
+		struct FnvHashBase {
+			[[gnu::pure]] [[gnu::always_inline]]
+			static uint32_t Calculate ( const char parChar, uint32_t parCrc );
+		};
+
+		//Update step: crc_32_tab[(crc ^ ch) & 0xff] ^ (crc >> 8)
+		template <uint32_t N, uint32_t I>
+		struct FnvHash : private FnvHashBase {
+			[[gnu::always_inline]]
+			static uint32_t Calculate ( const char (&str)[N], uint32_t crc ) {
+				const uint32_t prevcrc = FnvHash<N, I-1>::Calculate(str, crc);
+				return FnvHashBase::Calculate(str[I-1], prevcrc);
+			}
+		};
+		template <unsigned int N>
+		struct FnvHash<N, 1> : private FnvHashBase {
+			[[gnu::always_inline]]
+			static uint32_t Calculate ( const char (&str)[N], uint32_t crc ) {
+				return FnvHashBase::Calculate(str[0], crc);
+			}
+		};
+
+		class ConstCharWrapper {
+		public:
+			ConstCharWrapper ( const char* parStr ) : str(parStr) { }
+			const char* const str;
+		};
+	public:
+
+		StringCRC32 ( ConstCharWrapper parStr );
+
+		template <unsigned int N>
+		[[gnu::always_inline]]
+		StringCRC32 ( const char (&str)[N] ) :
+			m_hash(~FnvHash<N, N>::Calculate(str, 0xffffffff))
+		{
+		}
+
+		operator uint32_t ( void ) const { return m_hash; }
+
+	private:
+		uint32_t m_hash;
+
+	private:
+		//This is meant to represent a list of bits that are set to 1
+		template <int N, typename T>
+		struct BitArray {
+			enum { value = N };
+			typedef T Next;
+		};
+		//Polynomial from zlib: {0,1,2,4,5,7,8,10,11,12,16,22,23,26} or 0xedb88320UL
+//		for (int poly = 0, n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
+//			poly |= (z_crc_t)1 << (31 - p[n]);
+		typedef BitArray<0, BitArray<1, BitArray<2, BitArray<4, BitArray<5,
+				BitArray<7, BitArray<8, BitArray<10, BitArray<11, BitArray<12,
+				BitArray<16, BitArray<22, BitArray<23,
+				BitArray<26, nullptr_t> > > > > > > > > > > > > > PolynomialBits;
+		template <typename P, int M>
+		struct MakePolynomial {
+			enum { value = (1 << (M - P::value)) bitor MakePolynomial<typename P::Next, M>::value };
+		};
+		template <int M>
+		struct MakePolynomial<nullptr_t, M> {
+			enum { value = 0 };
+		};
+
+		//CRC32 algorithm from zlib:
+// 		for (int n = 0; n < 256; n++) {
+// 			c = n;
+// 			for (k = 0; k < 8; k++) c = c & 1 ? poly ^ (c >> 1) : c >> 1;
+// 			crc_table[n] = c;
+// 		}
+		template <int C, int S=8, uint32_t P=static_cast<uint32_t>(MakePolynomial<PolynomialBits, 31>::value)>
+		struct TableLookup {
+			static_assert(S > 1);
+			enum {
+				poly = P,
+				value = TableLookup<TableLookup<C, S-1, poly>::value, 1, poly>::value
+			};
+		};
+		template <int C, uint32_t P>
+		struct TableLookup<C, 1, P> {
+			enum {
+				poly = P,
+				value = ((C & 1) == 1 ? poly ^ (static_cast<uint32_t>(C) >> 1) : static_cast<uint32_t>(C) >> 1)
+			};
+		};
+	};
+
+	inline uint32_t StringCRC32::FnvHashBase::Calculate (const char parChar, uint32_t parCrc) {
+		static const uint32_t crc_32_tab[256] = { /* CRC polynomial 0xedb88320 */
+			0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
+			0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
+			0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
+			0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
+			0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
+			0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
+			0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
+			0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
+			0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
+			0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
+			0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
+			0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
+			0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
+			0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
+			0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
+			0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
+			0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
+			0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
+			0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
+			0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
+			0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
+			0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
+			0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
+			0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
+			0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
+			0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
+			0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
+			0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
+			0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
+			0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
+			0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
+			0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
+			0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
+			0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
+			0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
+			0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
+			0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
+			0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
+			0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
+			0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
+			0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
+			0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
+			0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
+		};
+		return crc_32_tab[(parCrc ^ parChar) & 0xff] ^ (parCrc >> 8);
+	}
+} //namespace duckcore
+
+#endif
diff --git a/include/wrenpp/vm.hpp b/include/wrenpp/vm.hpp
index f430e3c..39e0acc 100644
--- a/include/wrenpp/vm.hpp
+++ b/include/wrenpp/vm.hpp
@@ -20,12 +20,15 @@
 #include "has_method.hpp"
 #include "error_type.hpp"
 #include "handle.hpp"
+#include "StringCRC32.hpp"
 #include <memory>
 #include <tuple>
 #include <utility>
 #if __cpp_concepts >= 201907
 #	include <concepts>
 #endif
+#include <cstdint>
+#include <stdexcept>
 
 namespace wren {
 	class Configuration;
@@ -62,7 +65,8 @@ namespace wren {
 
 	class VM {
 	public:
-		template <typename T> VM (T* conf);
+		template <typename T, typename U> VM (T* conf, U* user_data);
+		template <typename T> VM (T* conf, std::nullptr_t);
 		VM (const VM&) = delete;
 		VM (VM&& other) = default;
 		~VM() noexcept;
@@ -95,14 +99,20 @@ namespace wren {
 		std::pair<const char*, int> slot_bytes (int slot_num);
 		void* slot_foreign (int slot_num);
 
+		template <typename U> U* user_data();
+		template <typename U> void set_user_data (U* user_data);
+		void set_user_data (std::nullptr_t);
+		bool has_user_data() const;
+
 	private:
 		struct LocalData;
 
-		VM (Configuration* conf, const detail::Callbacks&);
+		VM (Configuration* conf, const detail::Callbacks&, void* user_data, std::uint32_t user_data_type);
 		DynafuncMaker* dynafunc_maker();
-
-		template <typename T>
-		detail::Callbacks to_callbacks (T& conf);
+		std::uint32_t user_data_type() const;
+		void* void_user_data();
+		void set_user_data (void* user_data, std::uint32_t user_data_type);
+		template <typename T> detail::Callbacks to_callbacks (T& conf);
 
 		std::unique_ptr<LocalData> m_local;
 	};
@@ -131,6 +141,12 @@ namespace wren {
 				return (*M)(args...);
 			}
 		};
+
+		template <typename U>
+		[[gnu::const]]
+		inline constexpr std::uint32_t type_id() {
+			return duckcore::StringCRC32(__func__);
+		}
 	} //namespace detail
 
 	template <typename T>
@@ -167,9 +183,38 @@ namespace wren {
 		return ret;
 	}
 
+	template <typename U>
+	inline U* VM::user_data() {
+		if (user_data_type() != detail::type_id<U>()) {
+			throw std::runtime_error("Wrong user data type requested");
+		}
+		return reinterpret_cast<U*>(void_user_data());
+	}
+
+	template <typename U>
+	inline void VM::set_user_data (U* user_data) {
+		set_user_data(reinterpret_cast<void*>(user_data), detail::type_id<U>());
+	}
+
 	template <typename T>
-	inline VM::VM (T* conf) :
-		VM(static_cast<Configuration*>(conf), to_callbacks(*conf))
+	inline VM::VM (T* conf, std::nullptr_t) :
+		VM(
+			static_cast<Configuration*>(conf),
+			to_callbacks(*conf),
+			nullptr,
+			detail::type_id<std::nullptr_t>()
+		)
+	{
+	}
+
+	template <typename T, typename U>
+	inline VM::VM (T* conf, U* user_data) :
+		VM(
+			static_cast<Configuration*>(conf),
+			to_callbacks(*conf),
+			reinterpret_cast<void*>(user_data),
+			detail::type_id<U>()
+		)
 	{
 	}
 } //namespace wren
diff --git a/src/main.cpp b/src/main.cpp
index 8bf637f..f0d7bbe 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -84,7 +84,7 @@ int main() {
 	//typedef wren::ModuleAndName MN;
 
 	MyConfig config;
-	wren::VM vm(&config);
+	wren::VM vm(&config, nullptr);
 	vm.interpret("main", g_script);
 
 	wren::call<void>(vm, {"main", "the_user"}, "greet");
diff --git a/src/wren/vm.cpp b/src/wren/vm.cpp
index 96692dd..d0d01b7 100644
--- a/src/wren/vm.cpp
+++ b/src/wren/vm.cpp
@@ -120,9 +120,11 @@ namespace wren {
 		detail::Callbacks callbacks;
 		DynafuncMaker dynafunc;
 		WrenVM* wvm;
+		void* user_data;
+		std::uint32_t user_data_type;
 	};
 
-	VM::VM (Configuration* conf, const detail::Callbacks& cb) :
+	VM::VM (Configuration* conf, const detail::Callbacks& cb, void* user_data, std::uint32_t user_data_type) :
 		m_local(std::make_unique<LocalData>(cb))
 	{
 		WrenConfiguration wconf;
@@ -157,6 +159,9 @@ namespace wren {
 		m_local->wvm = wrenNewVM(&wconf);
 		if (not m_local->wvm)
 			throw std::runtime_error("Failed to initialize Wren VM");
+
+		m_local->user_data = user_data;
+		m_local->user_data_type = user_data_type;
 	}
 
 	VM::~VM() noexcept = default;
@@ -165,6 +170,19 @@ namespace wren {
 		return &m_local->dynafunc;
 	}
 
+	std::uint32_t VM::user_data_type() const {
+		return m_local->user_data_type;
+	}
+
+	void* VM::void_user_data() {
+		return m_local->user_data;
+	}
+
+	void VM::set_user_data (void* user_data, std::uint32_t user_data_type) {
+		m_local->user_data = user_data;
+		m_local->user_data_type = user_data_type;
+	}
+
 	void VM::interpret (const char* module_name, const char* script) {
 		using std::string;
 		using std::runtime_error;
@@ -183,6 +201,30 @@ namespace wren {
 			wrenReleaseHandle(m_local->wvm, handle);
 	}
 
+	void VM::set_slot_string (int slot_num, const char* value) {
+		wrenSetSlotString(m_local->wvm, slot_num, value);
+	}
+
+	void VM::set_slot_double (int slot_num, double value) {
+		wrenSetSlotDouble(m_local->wvm, slot_num, value);
+	}
+
+	void VM::set_slot_bool (int slot_num, bool value) {
+		wrenSetSlotBool(m_local->wvm, slot_num, value);
+	}
+
+	void VM::set_slot_null (int slot_num) {
+		wrenSetSlotNull(m_local->wvm, slot_num);
+	}
+
+	void VM::set_slot_bytes (int slot_num, const char* bytes, std::size_t length) {
+		wrenSetSlotBytes(m_local->wvm, slot_num, bytes, length);
+	}
+
+	void* VM::set_slot_new_foreign (int slot_num, int class_slot, std::size_t size) {
+		return wrenSetSlotNewForeign(m_local->wvm, slot_num, class_slot, size);
+	}
+
 	bool VM::slot_bool (int slot_num) {
 		assert(SlotType::Bool == slot_type(slot_num));
 		return wrenGetSlotBool(m_local->wvm, slot_num);
@@ -210,28 +252,13 @@ namespace wren {
 		return wrenGetSlotForeign(m_local->wvm, slot_num);
 	}
 
-	void VM::set_slot_string (int slot_num, const char* value) {
-		wrenSetSlotString(m_local->wvm, slot_num, value);
+	void VM::set_user_data (std::nullptr_t) {
+		m_local->user_data = nullptr;
+		m_local->user_data_type = detail::type_id<std::nullptr_t>();
 	}
 
-	void VM::set_slot_double (int slot_num, double value) {
-		wrenSetSlotDouble(m_local->wvm, slot_num, value);
-	}
-
-	void VM::set_slot_bool (int slot_num, bool value) {
-		wrenSetSlotBool(m_local->wvm, slot_num, value);
-	}
-
-	void VM::set_slot_null (int slot_num) {
-		wrenSetSlotNull(m_local->wvm, slot_num);
-	}
-
-	void VM::set_slot_bytes (int slot_num, const char* bytes, std::size_t length) {
-		wrenSetSlotBytes(m_local->wvm, slot_num, bytes, length);
-	}
-
-	void* VM::set_slot_new_foreign (int slot_num, int class_slot, std::size_t size) {
-		return wrenSetSlotNewForeign(m_local->wvm, slot_num, class_slot, size);
+	bool VM::has_user_data() const {
+		return nullptr != m_local->user_data;
 	}
 
 	void VM::ensure_slots (int num_slots) {