diff --git a/argus-core/src/expr.rs b/argus-core/src/expr.rs
index 831425a..a7b87ec 100644
--- a/argus-core/src/expr.rs
+++ b/argus-core/src/expr.rs
@@ -4,9 +4,11 @@ mod bool_ops;
 mod internal_macros;
 pub mod iter;
 mod num_ops;
+mod traits;
 
 pub use bool_ops::*;
 pub use num_ops::*;
+pub use traits::*;
 
 use crate::{ArgusResult, Error};
 
@@ -26,6 +28,21 @@ pub enum NumExpr {
     Div { dividend: Box<NumExpr>, divisor: Box<NumExpr> },
 }
 
+impl Expr for NumExpr {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn args(&self) -> Vec<&dyn Expr> {
+        match self {
+            NumExpr::Neg { arg } => vec![arg.as_ref()],
+            NumExpr::Add { args } | NumExpr::Mul { args } => args.iter().map(|arg| arg as &dyn Expr).collect(),
+            NumExpr::Div { dividend, divisor } => vec![dividend.as_ref(), divisor.as_ref()],
+            _ => vec![],
+        }
+    }
+}
+
 /// Types of comparison operations
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum Ordering {
@@ -46,6 +63,21 @@ pub enum BoolExpr {
     Or { args: Vec<BoolExpr> },
 }
 
+impl Expr for BoolExpr {
+    fn args(&self) -> Vec<&dyn Expr> {
+        match self {
+            BoolExpr::Cmp { op: _, lhs, rhs } => vec![lhs.as_ref(), rhs.as_ref()],
+            BoolExpr::Not { arg } => vec![arg.as_ref()],
+            BoolExpr::And { args } | BoolExpr::Or { args } => args.iter().map(|arg| arg as &dyn Expr).collect(),
+            _ => vec![],
+        }
+    }
+
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+}
+
 /// Expression builder
 ///
 /// The `ExprBuilder` is a factory structure that deals with the creation of
diff --git a/argus-core/src/expr/traits.rs b/argus-core/src/expr/traits.rs
new file mode 100644
index 0000000..50ddfa9
--- /dev/null
+++ b/argus-core/src/expr/traits.rs
@@ -0,0 +1,53 @@
+use std::any::Any;
+
+use super::iter::AstIter;
+
+/// A trait representing expressions
+pub trait Expr {
+    fn args(&self) -> Vec<&dyn Expr>;
+
+    fn as_any(&self) -> &dyn Any;
+
+    fn iter(&self) -> AstIter<'_>
+    where
+        Self: Sized,
+    {
+        AstIter::new(self)
+    }
+}
+
+impl dyn Expr {
+    pub fn downcast_expr_ref<T>(&self) -> Option<&T>
+    where
+        T: Any,
+    {
+        self.as_any().downcast_ref::<T>()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::{arbitrary, BoolExpr, NumExpr};
+    use super::*;
+    use proptest::prelude::*;
+
+    proptest! {
+        #[test]
+        fn downcast_expr_bool(bool_expr in arbitrary::bool_expr()) {
+            let expr_ref = bool_expr.as_ref() as &dyn Expr;
+
+            let downcast_ref = expr_ref.downcast_expr_ref::<BoolExpr>().unwrap();
+            assert_eq!(downcast_ref, bool_expr.as_ref());
+        }
+    }
+
+    proptest! {
+        #[test]
+        fn downcast_expr_num(num_expr in arbitrary::num_expr()) {
+            let expr_ref = num_expr.as_ref() as &dyn Expr;
+
+            let downcast_ref = expr_ref.downcast_expr_ref::<NumExpr>().unwrap();
+            assert_eq!(downcast_ref, num_expr.as_ref());
+        }
+    }
+}