diff --git a/src/elements/module.rs b/src/elements/module.rs
index 3e7af83..3a4f91a 100644
--- a/src/elements/module.rs
+++ b/src/elements/module.rs
@@ -14,6 +14,10 @@ impl Module {
     pub fn sections(&self) -> &[Section] {
         &self.sections
     }
+
+    pub fn sections_mut(&mut self) -> &mut Vec<Section> {
+        &mut self.sections
+    }
 }
 
 impl Deserialize for Module {
@@ -21,9 +25,7 @@ impl Deserialize for Module {
 
     fn deserialize<R: io::Read>(reader: &mut R) -> Result<Self, Self::Error> {
         let mut sections = Vec::new();
-
         let magic = Uint32::deserialize(reader)?;
-
         let version = Uint32::deserialize(reader)?;
 
         loop {
diff --git a/src/elements/section.rs b/src/elements/section.rs
index b6ee302..1c9895b 100644
--- a/src/elements/section.rs
+++ b/src/elements/section.rs
@@ -98,6 +98,29 @@ impl Deserialize for Section {
     }    
 }
 
+impl Serialize for Section {
+    type Error = Error;
+
+    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
+        match self {
+            Section::Custom(custom_section) => {
+                VarUint7::from(0x00).serialize(writer)?;
+                writer.write_all(&custom_section[..])?;
+            },
+            Section::Unparsed { id, payload } => {
+                VarUint7::from(id).serialize(writer)?;
+                writer.write_all(&payload[..])?;
+            },
+            Section::Type(type_section) => {
+                VarUint7::from(0x01).serialize(writer)?;
+                type_section.serialize(writer)?;
+            },
+            _ => unreachable!()
+        }
+        Ok(())
+    }
+}
+
 pub struct TypeSection(Vec<Type>);
 
 impl TypeSection {
@@ -117,6 +140,22 @@ impl Deserialize for TypeSection {
     }   
 }
 
+impl Serialize for TypeSection {
+    type Error = Error;
+    
+    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
+        let mut counted_writer = CountedWriter::new(writer);
+        let data = self.0;
+        let counted_list = CountedListWriter::<Type, _>(
+            data.len(),
+            data.into_iter().map(Into::into),
+        );
+        counted_list.serialize(&mut counted_writer)?;
+        counted_writer.done()?;
+        Ok(())
+    }    
+}
+
 pub struct ImportSection(Vec<ImportEntry>);
 
 impl ImportSection {
@@ -136,6 +175,22 @@ impl Deserialize for ImportSection {
     }   
 }
 
+impl Serialize for ImportSection {
+    type Error = Error;
+    
+    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
+        let mut counted_writer = CountedWriter::new(writer);
+        let data = self.0;
+        let counted_list = CountedListWriter::<ImportEntry, _>(
+            data.len(),
+            data.into_iter().map(Into::into),
+        );
+        counted_list.serialize(&mut counted_writer)?;
+        counted_writer.done()?;
+        Ok(())
+    }    
+}
+
 pub struct FunctionsSection(Vec<Func>);
 
 impl FunctionsSection {
@@ -159,6 +214,22 @@ impl Deserialize for FunctionsSection {
     }
 }
 
+impl Serialize for FunctionsSection {
+    type Error = Error;
+    
+    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
+        let mut counted_writer = CountedWriter::new(writer);
+        let data = self.0;
+        let counted_list = CountedListWriter::<VarUint32, _>(
+            data.len(),
+            data.into_iter().map(|func| func.type_ref().into())
+        );
+        counted_list.serialize(&mut counted_writer)?;
+        counted_writer.done()?;
+        Ok(())
+    }    
+}
+
 pub struct TableSection(Vec<TableType>);
 
 impl TableSection {
diff --git a/src/elements/types.rs b/src/elements/types.rs
index d3db2d5..3bae55d 100644
--- a/src/elements/types.rs
+++ b/src/elements/types.rs
@@ -1,5 +1,8 @@
 use std::io;
-use super::{Deserialize, Serialize, Error, VarUint7, VarInt7, VarUint1, CountedList};
+use super::{
+    Deserialize, Serialize, Error, VarUint7, VarInt7, VarUint1, CountedList, 
+    CountedListWriter
+};
 
 pub enum Type {
     Function(FunctionType),
@@ -13,6 +16,16 @@ impl Deserialize for Type {
     }
 }
 
+impl Serialize for Type {
+    type Error = Error;
+    
+    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
+        match self {
+            Type::Function(fn_type) => fn_type.serialize(writer)
+        }
+    }
+}
+
 #[derive(Clone, Copy, PartialEq, Debug)]
 pub enum ValueType {
     I32,
@@ -91,7 +104,6 @@ impl Serialize for BlockType {
     }
 }
 
-
 pub struct FunctionType {
     form: u8,
     params: Vec<ValueType>,
@@ -126,3 +138,27 @@ impl Deserialize for FunctionType {
         })
     }    
 }
+
+impl Serialize for FunctionType {
+    type Error = Error;
+    
+    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
+        VarUint7::from(self.form).serialize(writer)?;
+
+        let data = self.params;
+        let counted_list = CountedListWriter::<ValueType, _>(
+            data.len(),
+            data.into_iter().map(Into::into),
+        );
+        counted_list.serialize(writer)?;
+
+        if let Some(return_type) = self.return_type {
+            VarUint1::from(true).serialize(writer)?;
+            return_type.serialize(writer)?;
+        } else {
+            VarUint1::from(false).serialize(writer)?;
+        }
+
+        Ok(())
+    }
+}
\ No newline at end of file