diff --git a/scout-interpreter/src/lib.rs b/scout-interpreter/src/lib.rs
index ecb3766..814a42d 100644
--- a/scout-interpreter/src/lib.rs
+++ b/scout-interpreter/src/lib.rs
@@ -224,7 +224,7 @@ fn eval_statement<'a>(
                 Ok(Arc::new(Object::Null))
             }
             StmtKind::Func(def) => {
-                let lit = Object::Fn(def.args.clone(), def.body.clone());
+                let lit = Object::Fn(def.params.clone(), def.body.clone());
                 env.lock().await.set(&def.ident, Arc::new(lit)).await;
                 Ok(Arc::new(Object::Null))
             }
@@ -315,20 +315,31 @@ fn apply_call<'a>(
             obj_params.insert(0, obj);
         }
 
+        // Set var before match to avoid deadlock on env
         let env_res = env.lock().await.get(ident).await;
         match env_res {
             Some(obj) => match &*obj {
-                Object::Fn(idents, block) => {
-                    if idents.len() != obj_params.len() {
-                        return Err(EvalError::InvalidUsage("Non-matching arg counts".into()));
-                    }
-
+                Object::Fn(fn_params, block) => {
                     let mut scope = Env::default();
                     scope.add_outer(env.clone()).await;
-                    for i in 0..idents.len() {
-                        let id = &idents[i];
-                        let obj = &obj_params[i];
-                        scope.set(id, obj.clone()).await;
+                    for (i, fn_param) in fn_params.iter().enumerate() {
+                        let id = &fn_param.ident;
+                        match obj_params.get(i) {
+                            Some(provided) => {
+                                scope.set(id, provided.clone()).await;
+                            }
+                            None => match &fn_param.default {
+                                Some(def) => {
+                                    let obj_def =
+                                        eval_expression(def, crawler, env.clone(), results.clone())
+                                            .await?;
+                                    scope.set(id, obj_def).await;
+                                }
+                                None => {
+                                    return Err(EvalError::InvalidFnParams);
+                                }
+                            },
+                        }
                     }
 
                     let ev =
diff --git a/scout-interpreter/src/object.rs b/scout-interpreter/src/object.rs
index 5fc770a..acd6c3c 100644
--- a/scout-interpreter/src/object.rs
+++ b/scout-interpreter/src/object.rs
@@ -1,6 +1,6 @@
 use std::{collections::HashMap, fmt::Display, sync::Arc};
 
-use scout_parser::ast::{Block, Identifier};
+use scout_parser::ast::{Block, FnParam, Identifier};
 use serde_json::{json, Value};
 
 #[derive(Debug)]
@@ -12,7 +12,7 @@ pub enum Object {
     List(Vec<Arc<Object>>),
     Boolean(bool),
     Number(f64),
-    Fn(Vec<Identifier>, Block),
+    Fn(Vec<FnParam>, Block),
     Return(Arc<Object>),
 }
 
diff --git a/scout-parser/src/ast.rs b/scout-parser/src/ast.rs
index cfdeac3..70563d7 100644
--- a/scout-parser/src/ast.rs
+++ b/scout-parser/src/ast.rs
@@ -76,13 +76,29 @@ pub struct ElseLiteral {
 #[derive(Debug, PartialEq, Clone)]
 pub struct FuncDef {
     pub ident: Identifier,
-    pub args: Vec<Identifier>,
+    pub params: Vec<FnParam>,
     pub body: Block,
 }
 
 impl FuncDef {
-    pub fn new(ident: Identifier, args: Vec<Identifier>, body: Block) -> Self {
-        Self { ident, args, body }
+    pub fn new(ident: Identifier, params: Vec<FnParam>, body: Block) -> Self {
+        Self {
+            ident,
+            params,
+            body,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Clone)]
+pub struct FnParam {
+    pub ident: Identifier,
+    pub default: Option<ExprKind>,
+}
+
+impl FnParam {
+    pub fn new(ident: Identifier, default: Option<ExprKind>) -> Self {
+        Self { ident, default }
     }
 }
 
diff --git a/scout-parser/src/lib.rs b/scout-parser/src/lib.rs
index 0e38b1b..ffbc17a 100644
--- a/scout-parser/src/lib.rs
+++ b/scout-parser/src/lib.rs
@@ -1,8 +1,8 @@
 use std::collections::HashMap;
 
 use ast::{
-    ExprKind, ForLoop, FuncDef, HashLiteral, Identifier, IfElseLiteral, IfLiteral, Program,
-    StmtKind,
+    ExprKind, FnParam, ForLoop, FuncDef, HashLiteral, Identifier, IfElseLiteral, IfLiteral,
+    Program, StmtKind,
 };
 use scout_lexer::{Lexer, Token, TokenKind};
 
@@ -17,6 +17,7 @@ pub enum ParseError {
     UnexpectedToken(TokenKind, TokenKind),
     InvalidToken(TokenKind),
     InvalidNumber,
+    DefaultFnParamBefore,
 }
 
 pub struct Parser {
@@ -64,12 +65,26 @@ impl Parser {
                 self.expect_peek(TokenKind::LParen)?;
 
                 let mut args = Vec::new();
+                let mut has_defaults = false;
                 while self.peek.kind == TokenKind::Comma || self.peek.kind != TokenKind::RParen {
                     self.next_token();
                     match self.curr.kind {
                         TokenKind::Comma => {}
                         TokenKind::Ident => {
-                            args.push(Identifier::new(self.curr.literal.clone()));
+                            let ident = Identifier::new(self.curr.literal.clone());
+                            let mut default = None;
+                            if self.peek.kind == TokenKind::Assign {
+                                self.next_token();
+                                self.next_token();
+                                default = Some(self.parse_expr()?);
+                                has_defaults = true;
+                            } else if has_defaults {
+                                // Dont allow non-default params after default params.
+                                // If we dont disallow this then the interpreter will have a
+                                // hard time
+                                return Err(ParseError::DefaultFnParamBefore);
+                            }
+                            args.push(FnParam::new(ident, default));
                         }
                         _ => {
                             return Err(ParseError::InvalidToken(self.curr.kind));
@@ -470,6 +485,7 @@ mod tests {
             ExprKind::Str("a".into())
         )
     )]
+    #[test_case(r#"null"#, StmtKind::Expr(ExprKind::Null))]
     #[test_case(
         r#"for node in $$"a" do scrape {} end"#,
         StmtKind::ForLoop(
@@ -514,8 +530,20 @@ mod tests {
             FuncDef::new(
                 Identifier::new("f".into()),
                 vec![
-                    Identifier::new("a".into()),
-                    Identifier::new("b".into())
+                    FnParam::new(Identifier::new("a".into()), None),
+                    FnParam::new(Identifier::new("b".into()), None)
+                ],
+                Block::default()
+            )
+        )
+    )]
+    #[test_case(
+        r#"def f(a = null) do end"#,
+        StmtKind::Func(
+            FuncDef::new(
+                Identifier::new("f".into()),
+                vec![
+                    FnParam::new(Identifier::new("a".into()), Some(ExprKind::Null))
                 ],
                 Block::default()
             )