diff --git a/src/si/action.rs b/src/si/action.rs
new file mode 100644
index 00000000..d08c5fbf
--- /dev/null
+++ b/src/si/action.rs
@@ -0,0 +1,58 @@
+//! Action (base unit joule second, kg ⋅ m² ⋅ s⁻¹).
+
+quantity! {
+    /// Action (base unit joule second, kg ⋅ m² ⋅ s⁻¹).
+    quantity: Action; "action";
+    /// Dimension of action, L²MT⁻¹ (base unit joule second, kg ⋅ m² ⋅ s⁻¹).
+    dimension: ISQ<
+        P2,     // length
+        P1,     // mass
+        N1,     // time
+        Z0,     // electric current
+        Z0,     // thermodynamic temperature
+        Z0,     // amount of substance
+        Z0>;    // luminous intensity
+    units {
+        @joule_second: prefix!(none); "J · s", "joule second", "joule seconds";
+
+        /// Reduced Planck constant ħ.
+        @atomic_unit_of_action: 1.054_571_817_E-34; "ħ", "atomic unit of action",
+            "atomic units of action";
+        @reduced_planck_constant: 1.054_571_817_E-34; "ħ", "reduced planck constant",
+            "reduced planck constants";
+        @planck_constant: 6.626_070_15_E-34; "h", "planck constant", "planck constants";
+        @erg_second: 1.0_E-7; "erg · s", "erg second", "erg seconds";
+        @electronvolt_second: 1.602_176_634_E-19; "eV · s", "electronvolt second",
+            "electronvolt seconds";
+    }
+}
+
+#[cfg(test)]
+mod test {
+    storage_types! {
+        use crate::num::One;
+        use crate::si::quantities::*;
+        use crate::si::time as t;
+        use crate::si::energy as e;
+        use crate::si::action as act;
+        use crate::tests::Test;
+
+        #[test]
+        fn check_dimension() {
+            let _: Action<V> = Energy::new::<e::joule>(V::one())
+                * Time::new::<t::second>(V::one());
+        }
+
+        #[test]
+        fn check_units() {
+            test::<e::joule, t::second, act::joule_second>();
+            test::<e::erg, t::second, act::erg_second>();
+            test::<e::electronvolt, t::second, act::electronvolt_second>();
+
+            fn test<E: e::Conversion<V>, T: t::Conversion<V>, ACT: act::Conversion<V>>() {
+                Test::assert_approx_eq(&Action::new::<ACT>(V::one()),
+                    &(Energy::new::<E>(V::one()) * Time::new::<T>(V::one())));
+            }
+        }
+    }
+}
diff --git a/src/si/mod.rs b/src/si/mod.rs
index 9e7d9ff0..24a38df8 100644
--- a/src/si/mod.rs
+++ b/src/si/mod.rs
@@ -47,6 +47,7 @@ system! {
     units: SI {
         absement::Absement,
         acceleration::Acceleration,
+        action::Action,
         amount_of_substance::AmountOfSubstance,
         angle::Angle,
         angular_acceleration::AngularAcceleration,