diff --git a/dust-lang/src/abstract_tree.rs b/dust-lang/src/abstract_tree.rs
index b86683d..b20bd06 100644
--- a/dust-lang/src/abstract_tree.rs
+++ b/dust-lang/src/abstract_tree.rs
@@ -207,8 +207,36 @@ impl BuiltInFunction {
                     Err(BuiltInFunctionError::WrongNumberOfValueArguments)
                 }
             }
-            BuiltInFunction::IsOdd => todo!(),
-            BuiltInFunction::Length => todo!(),
+            BuiltInFunction::IsOdd => {
+                if let Some(value_arguments) = value_arguments {
+                    if value_arguments.len() == 1 {
+                        if let Some(integer) = value_arguments[0].as_integer() {
+                            Ok(Value::boolean(integer % 2 != 0))
+                        } else {
+                            Err(BuiltInFunctionError::ExpectedInteger)
+                        }
+                    } else {
+                        Err(BuiltInFunctionError::WrongNumberOfValueArguments)
+                    }
+                } else {
+                    Err(BuiltInFunctionError::WrongNumberOfValueArguments)
+                }
+            }
+            BuiltInFunction::Length => {
+                if let Some(value_arguments) = value_arguments {
+                    if value_arguments.len() == 1 {
+                        if let Some(list) = value_arguments[0].as_list() {
+                            Ok(Value::integer(list.len() as i64))
+                        } else {
+                            Err(BuiltInFunctionError::ExpectedInteger)
+                        }
+                    } else {
+                        Err(BuiltInFunctionError::WrongNumberOfValueArguments)
+                    }
+                } else {
+                    Err(BuiltInFunctionError::WrongNumberOfValueArguments)
+                }
+            }
         }
     }
 
diff --git a/dust-lang/src/parse.rs b/dust-lang/src/parse.rs
index 2437146..026f523 100644
--- a/dust-lang/src/parse.rs
+++ b/dust-lang/src/parse.rs
@@ -283,6 +283,66 @@ impl<'src> Parser<'src> {
                     left_span,
                 ))
             }
+            (Token::IsOdd, left_span) => {
+                self.next_token()?;
+
+                if let (Token::LeftParenthesis, _) = self.current {
+                    self.next_token()?;
+                } else {
+                    return Err(ParseError::ExpectedOpeningParenthesis {
+                        actual: self.current.0.clone(),
+                        span: self.current.1,
+                    });
+                }
+
+                if let (Token::RightParenthesis, _) = self.current {
+                    self.next_token()?;
+                } else {
+                    return Err(ParseError::ExpectedClosingParenthesis {
+                        actual: self.current.0.clone(),
+                        span: self.current.1,
+                    });
+                }
+
+                Ok(Node::new(
+                    Statement::BuiltInFunctionCall {
+                        function: BuiltInFunction::IsOdd,
+                        type_arguments: None,
+                        value_arguments: None,
+                    },
+                    left_span,
+                ))
+            }
+            (Token::Length, left_span) => {
+                self.next_token()?;
+
+                if let (Token::LeftParenthesis, _) = self.current {
+                    self.next_token()?;
+                } else {
+                    return Err(ParseError::ExpectedOpeningParenthesis {
+                        actual: self.current.0.clone(),
+                        span: self.current.1,
+                    });
+                }
+
+                if let (Token::RightParenthesis, _) = self.current {
+                    self.next_token()?;
+                } else {
+                    return Err(ParseError::ExpectedClosingParenthesis {
+                        actual: self.current.0.clone(),
+                        span: self.current.1,
+                    });
+                }
+
+                Ok(Node::new(
+                    Statement::BuiltInFunctionCall {
+                        function: BuiltInFunction::Length,
+                        type_arguments: None,
+                        value_arguments: None,
+                    },
+                    left_span,
+                ))
+            }
             _ => Err(ParseError::UnexpectedToken(self.current.0.clone())),
         }
     }