diff --git a/crates/node-types/src/action.rs b/crates/node-types/src/action.rs
new file mode 100644
index 0000000..09667d2
--- /dev/null
+++ b/crates/node-types/src/action.rs
@@ -0,0 +1,23 @@
+//! # Action
+//!
+//! Actions use predicates to generate solutions.
+
+use essential_types::{PredicateAddress, Value};
+
+/// Actions represent are used as the input to solve a predicate
+/// and generate a [`Solution`](essential_types::Solution).
+pub struct Action {
+    /// The predicate that will be solved by this action.
+    pub predicate_to_solve: PredicateAddress,
+    /// The inputs to the predicate.
+    pub inputs: Vec<Value>,
+}
+
+/// An atomic unordered set of actions.
+/// These all occur at the same time.
+/// It is invalid for the solutions generated
+/// by these actions to mutate the same keys.
+pub struct ActionSet {
+    /// An unordered set of actions.
+    pub actions: Vec<Action>,
+}
diff --git a/crates/node-types/src/lib.rs b/crates/node-types/src/lib.rs
index 6d0a94d..10f8713 100644
--- a/crates/node-types/src/lib.rs
+++ b/crates/node-types/src/lib.rs
@@ -14,6 +14,7 @@ use essential_types::{
 };
 use serde::{Deserialize, Serialize};
 
+pub mod action;
 pub mod block;
 
 /// Wrappers around tokio's `watch` channel for notifying of new blocks.