diff --git a/Statlib.lean b/Statlib.lean
index a5f1af4..9e4be37 100644
--- a/Statlib.lean
+++ b/Statlib.lean
@@ -137,6 +137,7 @@ import Statlib.ForMathlib.Probability.StrongLaw
 import Statlib.ForMathlib.Topology.Order.MonotoneConvergence
 import Statlib.Inference.Inference
 import Statlib.Inference.QMD
+import Statlib.PValues.PValue
 import Statlib.Testing.Binary
 import Statlib.Testing.BinaryRenyi
 import Statlib.Testing.ChangeMeasure
diff --git a/Statlib/PValues/PValue.lean b/Statlib/PValues/PValue.lean
new file mode 100644
index 0000000..7f9f2db
--- /dev/null
+++ b/Statlib/PValues/PValue.lean
@@ -0,0 +1,37 @@
+/-
+Copyright (c) 2026 Rajarshi Mukherjee. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Rajarshi Mukherjee
+-/
+
+module
+
+public import Mathlib.MeasureTheory.Measure.ProbabilityMeasure
+
+/-!
+# P-values for composite null hypotheses
+
+A p-value is a measurable function taking values in [0, 1] that
+uniformly has prescribed tail probability
+under every probability measure in the null hypothesis.
+-/
+
+@[expose] public section
+
+open scoped ENNReal
+
+open MeasureTheory
+
+variable {𝓧 : Type*} [m𝓧 : MeasurableSpace 𝓧]
+
+namespace ProbabilityTheory
+
+/-- A valid p-value for the composite null hypothesis `S`. -/
+structure IsPValue (Pval : 𝓧 → ℝ≥0∞)
+    (S : Set (ProbabilityMeasure 𝓧)) : Prop where
+  measurable : Measurable Pval := by fun_prop
+  le_one : ∀ ω, Pval ω ≤ 1
+  s_uniform : ∀ μ ∈ S, ∀ α : ℝ≥0∞,
+    (μ : Measure 𝓧) {ω | Pval ω ≤ α} ≤ α
+
+end ProbabilityTheory