diff --git a/src/function.rs b/src/function.rs
index e69de29..a9077e7 100644
--- a/src/function.rs
+++ b/src/function.rs
@@ -0,0 +1,70 @@
+use std::iter::Peekable;
+use std::vec::IntoIter;
+
+use crate::common::{Pos, Scope, Symbol};
+use crate::args::{eat_func_args, FuncArgs};
+use crate::utils::devour_whitespace;
+use crate::{Token, TokenKind};
+
+#[derive(Debug, Clone)]
+pub(crate) struct Function {
+    scope: Scope,
+    args: FuncArgs,
+    body: Peekable<IntoIter<Token>>,
+}
+
+
+impl Function {
+    pub fn new(scope: Scope, args: FuncArgs, body: Vec<Token>) -> Self {
+        let body = body.into_iter().peekable();
+        Function { scope, args, body }
+    }
+
+    pub fn decl_from_tokens<I: Iterator<Item = Token>>(
+        toks: &mut Peekable<I>,
+        scope: &Scope,
+    ) -> Result<(String, Function), (Pos, String)> {
+        let Token { pos, kind } = toks
+            .next()
+            .expect("this must exist because we have already peeked");
+        devour_whitespace(toks);
+        let name = match kind {
+            TokenKind::Ident(s) => s,
+            _ => {
+                return Err((
+                    pos,
+                    String::from("expected identifier after function declaration"),
+                ))
+            }
+        };
+        devour_whitespace(toks);
+        let args = match toks.next() {
+            Some(Token {
+                kind: TokenKind::Symbol(Symbol::OpenParen),
+                ..
+            }) => eat_func_args(toks),
+            _ => return Err((pos, String::from("expected `(` after function declaration"))),
+        };
+
+        let mut nesting = 1;
+        let mut body = Vec::new();
+
+        while nesting > 0 {
+            if let Some(tok) = toks.next() {
+                match &tok.kind {
+                    TokenKind::Symbol(Symbol::OpenCurlyBrace)
+                    // interpolation token eats the opening brace but not the closing
+                    | TokenKind::Interpolation => nesting += 1,
+                    TokenKind::Symbol(Symbol::CloseCurlyBrace) => nesting -= 1,
+                    _ => {}
+                }
+                body.push(tok)
+            } else {
+                return Err((pos, String::from("unexpected EOF")));
+            }
+        }
+
+        Ok((name, Function::new(scope.clone(), args, body)))
+    }
+
+}
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index 1490e10..a755a30 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -52,6 +52,7 @@ use crate::common::{Keyword, Op, Pos, Scope, Symbol, Whitespace};
 use crate::css::Css;
 use crate::error::SassError;
 use crate::format::PrettyPrinter;
+use crate::function::Function;
 use crate::imports::import;
 use crate::lexer::Lexer;
 use crate::mixin::{eat_include, Mixin};
@@ -201,6 +202,7 @@ enum Expr {
     VariableDecl(String, Vec<Token>),
     /// A mixin declaration `@mixin foo {}`
     MixinDecl(String, Mixin),
+    FunctionDecl(String, Function),
     /// An include statement `@include foo;`
     Include(Vec<Stmt>),
     /// A multiline comment: `/* foobar */`
@@ -398,11 +400,6 @@ impl<'a> StyleSheetParser<'a> {
                     rules.extend(new_rules);
                     self.global_scope.merge(new_scope);
                 }
-                TokenKind::AtRule(AtRuleKind::Mixin) => {
-                    let (name, mixin) =
-                        Mixin::decl_from_tokens(&mut self.lexer, &self.global_scope).unwrap();
-                    self.global_scope.mixins.insert(name, mixin);
-                }
                 TokenKind::AtRule(_) => {
                     if let Some(Token {
                         kind: TokenKind::AtRule(ref rule),
@@ -411,10 +408,10 @@ impl<'a> StyleSheetParser<'a> {
                     {
                         match eat_at_rule(rule, pos, &mut self.lexer, &self.global_scope) {
                             AtRule::Mixin(name, mixin) => {self.global_scope.mixins.insert(name, mixin);},
+                            AtRule::Function(name, func) => {self.global_scope.functions.insert(name, func);},
                             AtRule::Error(pos, message) => self.error(pos, &message),
                             AtRule::Warn(pos, message) => self.warn(pos, &message),
                             AtRule::Debug(pos, message) => self.debug(pos, &message),
-                            _ => todo!(),
                         }
                     }
                 }
@@ -437,6 +434,9 @@ impl<'a> StyleSheetParser<'a> {
                 Expr::MixinDecl(name, mixin) => {
                     scope.mixins.insert(name, mixin);
                 }
+                Expr::FunctionDecl(name, func) => {
+                    scope.functions.insert(name, func);
+                }
                 Expr::Selector(s) => {
                     self.scope += 1;
                     let rules = self.eat_rules(&super_selector.zip(&s), scope);
@@ -512,7 +512,7 @@ fn eat_at_rule<I: Iterator<Item = Token>>(
                 Ok(m) => m,
                 Err(e) => return AtRule::Error(e.0, e.1),
             };
-            Ok(Expr::MixinDecl(name, mixin))
+            AtRule::Function(name, mixin)
         }
         AtRuleKind::Use => todo!("@use not yet implemented"),
         AtRuleKind::Annotation => todo!("@annotation not yet implemented"),
@@ -525,7 +525,6 @@ fn eat_at_rule<I: Iterator<Item = Token>>(
         AtRuleKind::For => todo!("@for not yet implemented"),
         AtRuleKind::While => todo!("@while not yet implemented"),
         AtRuleKind::Media => todo!("@media not yet implemented"),
-        AtRuleKind::Function => todo!("@function not yet implemented"),
         AtRuleKind::Keyframes => todo!("@keyframes not yet implemented"),
         _ => todo!("encountered unimplemented at rule"),
     }
@@ -620,10 +619,10 @@ pub(crate) fn eat_expr<I: Iterator<Item = Token>>(
                 {
                     return match eat_at_rule(rule, pos, toks, scope) {
                         AtRule::Mixin(name, mixin) => Ok(Some(Expr::MixinDecl(name, mixin))),
+                        AtRule::Function(name, func) => Ok(Some(Expr::FunctionDecl(name, func))),
                         AtRule::Debug(a, b) => Ok(Some(Expr::Debug(a, b))),
                         AtRule::Warn(a, b) => Ok(Some(Expr::Warn(a, b))),
                         AtRule::Error(a, b) => Err((a, b)),
-                        _ => todo!(),
                     }
                 }
             }
diff --git a/src/mixin.rs b/src/mixin.rs
index 7051896..af3f562 100644
--- a/src/mixin.rs
+++ b/src/mixin.rs
@@ -94,7 +94,7 @@ impl Mixin {
         while let Some(expr) = eat_expr(&mut self.body, &self.scope, super_selector)? {
             match expr {
                 Expr::Style(s) => stmts.push(Stmt::Style(s)),
-                Expr::Include(..) | Expr::MixinDecl(..) | Expr::Debug(..) | Expr::Warn(..) => {
+                Expr::Include(..) | Expr::MixinDecl(..) | Expr::FunctionDecl(..) | Expr::Debug(..) | Expr::Warn(..) => {
                     todo!()
                 }
                 Expr::Selector(selector) => {