diff --git a/Cargo.toml b/Cargo.toml
index 8681c3d..2d96aba 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,8 +24,12 @@ byteorder = { version = "1.0", default-features = false }
 hashmap_core = { version = "0.1.9", optional = true }
 memory_units = "0.3.0"
 libm = { version = "0.1.2", optional = true }
+wasmi-derive = { version = "0.1", path = "derive" }
 
 [dev-dependencies]
 assert_matches = "1.1"
 rand = "0.4.2"
 wabt = "0.6"
+
+[workspace]
+members = ["derive"]
diff --git a/derive/Cargo.toml b/derive/Cargo.toml
new file mode 100644
index 0000000..a8f7f91
--- /dev/null
+++ b/derive/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "wasmi-derive"
+version = "0.1.0"
+authors = ["Sergey Pepyakin <sergei@parity.io>"]
+edition = "2018"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "0.6"
+syn = { version = "0.15.0", features = ['full'] }
+proc-macro2 = "0.4.9"
diff --git a/derive/src/codegen.rs b/derive/src/codegen.rs
new file mode 100644
index 0000000..59fb7cd
--- /dev/null
+++ b/derive/src/codegen.rs
@@ -0,0 +1,124 @@
+use crate::model::{ExtDefinition, ExternalFunc};
+use proc_macro2::{Ident, Literal, Span, TokenStream};
+use quote::{quote, quote_spanned, ToTokens};
+
+
+pub fn codegen(ext_def: &ExtDefinition, to: &mut TokenStream) {
+    let mut externals = TokenStream::new();
+    let mut module_resolver = TokenStream::new();
+
+    // TODO: Come up with a name.
+    let mut new_name = "_WASMI_IMPLS_".to_string();
+	new_name.push_str("NAME".to_string().trim_start_matches("r#"));
+	let dummy_const = Ident::new(&new_name, Span::call_site());
+
+    derive_externals(ext_def, &mut externals);
+    derive_module_resolver(ext_def, &mut module_resolver);
+
+    (quote! {
+        const #dummy_const: () = {
+			extern crate wasmi as _wasmi;
+
+            use _wasmi::{
+                Trap, RuntimeValue, RuntimeArgs, Externals,
+                derive_support::WasmResult,
+            };
+
+            #externals
+            #module_resolver
+        };
+    }).to_tokens(to);
+}
+
+fn gen_dispatch_func_arm(func: &ExternalFunc) -> TokenStream {
+    let index = func.index as usize;
+    let name = Ident::new(&func.name, Span::call_site());
+    let return_ty_span = func.return_ty.clone().unwrap_or_else(|| Span::call_site());
+
+    let mut args = vec![];
+    let mut unmarshall_args = TokenStream::new();
+    for (i, arg_span) in func.args.iter().cloned().enumerate() {
+        let mut arg_name = "arg".to_string();
+        arg_name.push_str(&i.to_string());
+        let arg_name = Ident::new(&arg_name, arg_span.clone());
+
+        (quote_spanned! {arg_span=>
+            let #arg_name =
+                args.next()
+                    .and_then(|rt_val| rt_val.try_into())
+                    .unwrap();
+        }).to_tokens(&mut unmarshall_args);
+
+        args.push(quote_spanned! {arg_span=> #arg_name });
+    }
+
+    let prologue = quote! {
+        let mut args = args.as_ref().iter();
+        #unmarshall_args
+    };
+    let epilogue = quote_spanned! {return_ty_span=>
+        WasmResult::to_wasm_result(r)
+    };
+
+    (quote! {
+        #index => {
+            #prologue
+            let r = self.#name( #(#args),* );
+            #epilogue
+        }
+    })
+
+    // let body = $crate::wasm_utils::constrain_closure::<
+    //     <$returns as $crate::wasm_utils::ConvertibleToWasm>::NativeType, _
+    // >(|| {
+    //     unmarshall_args!($body, $objectname, $args_iter, $( $names : $params ),*)
+    // });
+    // let r = body()?;
+    // return Ok(Some({ use $crate::wasm_utils::ConvertibleToWasm; r.to_runtime_value() }))
+}
+
+fn derive_externals(ext_def: &ExtDefinition, to: &mut TokenStream) {
+    let (impl_generics, ty_generics, where_clause) = ext_def.generics.split_for_impl();
+    let ty = &ext_def.ty;
+
+    let mut match_arms = vec![];
+    for func in &ext_def.funcs {
+        match_arms.push(gen_dispatch_func_arm(func));
+    }
+
+    (quote::quote! {
+        impl #impl_generics Externals for #ty #where_clause {
+            fn invoke_index(
+                &mut self,
+                index: usize,
+                args: RuntimeArgs,
+            ) -> Result<Option<RuntimeValue>, Trap> {
+                match index {
+                    #(#match_arms),*
+                    _ => panic!("fn with index {} is undefined", index),
+                }
+            }
+
+            // ...
+        }
+    }).to_tokens(to);
+}
+
+fn derive_module_resolver(ext_def: &ExtDefinition, to: &mut TokenStream) {
+    (quote::quote! {
+        impl #impl_generics ModuleImportResolver for #ty #where_clause {
+            fn invoke_index(
+                &mut self,
+                index: usize,
+                args: RuntimeArgs,
+            ) -> Result<Option<RuntimeValue>, Trap> {
+                match index {
+                    #(#match_arms),*
+                    _ => panic!("fn with index {} is undefined", index),
+                }
+            }
+
+            // ...
+        }
+    }).to_tokens(to);
+}
diff --git a/derive/src/lib.rs b/derive/src/lib.rs
new file mode 100644
index 0000000..eca13e2
--- /dev/null
+++ b/derive/src/lib.rs
@@ -0,0 +1,34 @@
+extern crate proc_macro;
+
+mod model;
+mod parser;
+mod codegen;
+
+use proc_macro::TokenStream;
+
+#[proc_macro_attribute]
+pub fn derive_externals(attr: TokenStream, input: TokenStream) -> TokenStream {
+    let mut input: proc_macro2::TokenStream = input.into();
+
+    let ext_def = parser::parse(input.clone()).unwrap();
+    codegen::codegen(&ext_def, &mut input);
+
+    // We need to generate two types:
+    // - Externals
+    // - ModuleImportResolver
+
+    // - for each of declared method collect it's name and it's signature.
+    // - assign a method index for each method
+    // - generate a switch for `Externals` that takes the input `index` and jumps
+    //   on the corresponding match arm, which the wrapper.
+    //   The wrapper decodes arguments, calls to the function and handles the result.
+    // - generate a switch / ifs chain for `ModuleImportResolver`. In each arm it checks if the function
+    //   has an appropriate arguments, and if so allocates a host function with the corresponding index.
+    //
+    // and we will then need to return both the original implementation and the generated implementation
+    // of externals.
+
+    // println!("{:?}", quote::quote! { #input }.to_string());
+    let input = input.into();
+    input
+}
diff --git a/derive/src/model.rs b/derive/src/model.rs
new file mode 100644
index 0000000..acd2481
--- /dev/null
+++ b/derive/src/model.rs
@@ -0,0 +1,39 @@
+pub enum ValueType {
+    I32,
+    I64,
+    F32,
+    F64,
+}
+
+pub struct Signature {
+    pub params: Vec<ValueType>,
+    pub return_ty: Option<ValueType>,
+}
+
+pub struct Param {
+    span: proc_macro2::Span,
+    generated_name: String,
+}
+
+pub struct ExternalFunc {
+    /// Assigned index of this function.
+    pub index: u32,
+    pub name: String,
+    // TODO: Rename args to params
+    pub args: Vec<Param>,
+    pub return_ty: Option<proc_macro2::Span>,
+    // TODO: remove
+    pub arity: usize,
+}
+
+/// The core structure that contains the list of all functions
+/// and the data required for implementing a trait.
+pub struct ExtDefinition {
+    /// List of all external functions.
+    pub funcs: Vec<ExternalFunc>,
+    /// The generics required to implement a trait for this type.
+    pub generics: syn::Generics,
+    /// The type declaration to implement to implement a trait, most typically
+    /// represented by a structure.
+    pub ty: Box<syn::Type>,
+}
diff --git a/derive/src/parser.rs b/derive/src/parser.rs
new file mode 100644
index 0000000..a38d17e
--- /dev/null
+++ b/derive/src/parser.rs
@@ -0,0 +1,46 @@
+use crate::model::{self, ExtDefinition, ExternalFunc};
+use syn::{ItemImpl, ImplItem, ImplItemMethod, FnArg, ReturnType};
+use syn::spanned::Spanned;
+
+/// Parse an incoming stream of tokens into a list of external functions.
+pub fn parse(input: proc_macro2::TokenStream) -> Result<ExtDefinition, ()> {
+    let item_impl = syn::parse2::<syn::ItemImpl>(input).map_err(|_| ())?;
+
+    let mut funcs = vec![];
+
+    for item in item_impl.items {
+        match item {
+            ImplItem::Method(ImplItemMethod {
+                sig,
+                ..
+            }) => {
+                let index = funcs.len() as u32;
+
+                // self TODO: handle this properly
+                let args = sig.decl.inputs.iter().skip(1).enumerate().map(|input| {
+                    input.span()
+                }).collect::<Vec<_>>();
+
+                let return_ty = match sig.decl.output {
+                    ReturnType::Default => None,
+                    ReturnType::Type(_, ty) => Some(ty.span()),
+                };
+
+                funcs.push(ExternalFunc {
+                    index,
+                    name: sig.ident.to_string(),
+                    args,
+                    return_ty,
+                    arity: sig.decl.inputs.len() - 1, // self TODO: handle this properly
+                });
+            },
+            _ => {},
+        }
+    }
+
+    Ok(ExtDefinition {
+        funcs,
+        generics: item_impl.generics.clone(),
+        ty: item_impl.self_ty.clone(),
+    })
+}
diff --git a/src/derive_support.rs b/src/derive_support.rs
new file mode 100644
index 0000000..830fbe1
--- /dev/null
+++ b/src/derive_support.rs
@@ -0,0 +1,48 @@
+use {ValueType, RuntimeValue, Trap};
+
+pub trait ConvertibleToWasm {
+    const VALUE_TYPE: ValueType;
+    type NativeType;
+    fn to_runtime_value(self) -> RuntimeValue;
+}
+
+impl ConvertibleToWasm for i32 { type NativeType = i32; const VALUE_TYPE: ValueType = ValueType::I32; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I32(self) } }
+impl ConvertibleToWasm for u32 { type NativeType = u32; const VALUE_TYPE: ValueType = ValueType::I32; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I32(self as i32) } }
+impl ConvertibleToWasm for i64 { type NativeType = i64; const VALUE_TYPE: ValueType = ValueType::I64; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I64(self) } }
+impl ConvertibleToWasm for u64 { type NativeType = u64; const VALUE_TYPE: ValueType = ValueType::I64; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I64(self as i64) } }
+impl ConvertibleToWasm for isize { type NativeType = i32; const VALUE_TYPE: ValueType = ValueType::I32; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I32(self as i32) } }
+impl ConvertibleToWasm for usize { type NativeType = u32; const VALUE_TYPE: ValueType = ValueType::I32; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I32(self as u32 as i32) } }
+impl<T> ConvertibleToWasm for *const T { type NativeType = u32; const VALUE_TYPE: ValueType = ValueType::I32; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I32(self as isize as i32) } }
+impl<T> ConvertibleToWasm for *mut T { type NativeType = u32; const VALUE_TYPE: ValueType = ValueType::I32; fn to_runtime_value(self) -> RuntimeValue { RuntimeValue::I32(self as isize as i32) } }
+
+pub trait WasmResult {
+    fn to_wasm_result(self) -> Result<Option<RuntimeValue>, Trap>;
+}
+
+impl WasmResult for () {
+    fn to_wasm_result(self) -> Result<Option<RuntimeValue>, Trap> {
+        Ok(None)
+    }
+}
+
+impl<R: ConvertibleToWasm, E: Into<Trap>> WasmResult for Result<R, E>  {
+    fn to_wasm_result(self) -> Result<Option<RuntimeValue>, Trap> {
+        self
+            .map(|v| Some(v.to_runtime_value()))
+            .map_err(Into::into)
+    }
+}
+
+impl<E: Into<Trap>> WasmResult for Result<(), E>  {
+    fn to_wasm_result(self) -> Result<Option<RuntimeValue>, Trap> {
+        self
+            .map(|_| None)
+            .map_err(Into::into)
+    }
+}
+
+impl<R: ConvertibleToWasm> WasmResult for R {
+    fn to_wasm_result(self) -> Result<Option<RuntimeValue>, Trap> {
+        Ok(Some(self.to_runtime_value()))
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index f92c4d3..6aeaf83 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -396,6 +396,9 @@ mod types;
 mod validation;
 mod value;
 
+// TODO: feature
+pub mod derive_support;
+
 #[cfg(test)]
 mod tests;
 
diff --git a/tests/derives.rs b/tests/derives.rs
new file mode 100644
index 0000000..82fb150
--- /dev/null
+++ b/tests/derives.rs
@@ -0,0 +1,40 @@
+extern crate wasmi_derive;
+extern crate wasmi;
+
+use wasmi_derive::derive_externals;
+use wasmi::HostError;
+use std::fmt;
+
+#[derive(Debug)]
+struct NoInfoError;
+impl HostError for NoInfoError {}
+impl fmt::Display for NoInfoError {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		write!(f, "NoInfoError")
+	}
+}
+
+struct NonStaticExternals<'a> {
+    state: &'a mut usize,
+}
+
+#[derive_externals]
+impl<'a> NonStaticExternals<'a> {
+    pub fn hello(&self, a: u32, b: u32) -> u32 {
+        a + b
+    }
+
+    pub fn increment(&mut self) {
+        *self.state += 1;
+    }
+
+    pub fn traps(&self) -> Result<(), NoInfoError> {
+        Err(NoInfoError)
+    }
+
+    pub fn fart(&self, inbound_fart: Fart) -> Result<Fart, NoInfoError> {
+        Ok(inbound_fart)
+    }
+}
+
+pub struct Fart;