diff --git a/CHANGELOG.md b/CHANGELOG.md
index 46783a2..ae165b4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,8 @@ All notable changes to Celerity are documented here. This project follows [Keep
 
 ### Added
 
+- `ContainsValue(TValue? value)` on `IntDictionary<TValue, THasher>`, `LongDictionary<TValue, THasher>`, and `CelerityDictionary<TKey, TValue, THasher>` — BCL-parity `O(n)` linear scan that returns `true` if any entry's value equals `value` under `EqualityComparer<TValue>.Default`, matching `Dictionary<TKey, TValue>.ContainsValue(TValue)`. The scan walks the probe table (skipping `EMPTY_KEY` / `default(TKey)` slots so the empty `default(TValue)` payload there is not mistaken for a real entry) and, when present, the out-of-band zero-key / default-key slot. No allocation on the hot path beyond the cached `EqualityComparer<TValue>.Default` access. Closes #73.
+- `ContainsValueTests` — coverage on all three dictionaries: empty-map false return, match in a regular slot, match found only in the zero-key / default-key / null-string-key slot, missing-value false return, default-`TValue` (`0`) lookup on both empty and populated dictionaries (regression check that `EMPTY_KEY` slots are skipped and not reported as `0` matches), `null`-`TValue` lookup on a reference-type value, duplicate values short-circuiting, post-resize correctness across a 100-entry insert from a tiny initial capacity, and post-`Remove` / post-`Clear` invalidation.
 - `IEnumerable<T>` constructor on `IntSet`, `IntSet<THasher>`, and `CeleritySet<T, THasher>` (and the `IntSet` convenience subclass), mirroring the dictionary `IEnumerable<KeyValuePair<,>>` ctor shipped in 1.1.2. Throws `ArgumentNullException` on a null source. Unlike the dictionary ctor, duplicate elements (including duplicate `default(T)` / zero entries) are silently deduplicated to match BCL `HashSet<T>(IEnumerable<T>)` semantics — sets do not have a duplicate-key contract. When the source implements `ICollection<T>`, its `Count` is used to size the backing storage; otherwise the caller-supplied `capacity` parameter is used. The out-of-band `default(T)` / zero slot is populated correctly when the source contains it. Closes the last set-side API-parity gap for milestone 1.1.0 and unblocks future `IReadOnlySet<T>` work. Closes #69.
 - `SetIEnumerableConstructorTests` — coverage for both sets: null-source and invalid-load-factor validation, empty sources, array / list / non-collection enumerable sources, duplicate-element silent dedupe (including duplicate zero / `null` / `default(T)` entries), zero-element / null-reference-element capture, 500-entry large-source round-trip, source-independence after construction, caller-specified capacity dominating the source count, cross-set copy (`CeleritySet` from an `IntSet` enumeration), and an open-generic `IntSet<Int32WangNaiveHasher>` smoke test.
 - `README.md` — new "Choosing a collection" section: a decision table mapping common workloads (`int`-keyed, `long`-keyed, `Guid` / `string` / other-keyed dictionaries, the two set shapes) onto the right Celerity type, plus a short note on picking a hasher and an honest "where Celerity is not the right answer today" list (concurrent access, mutable `IDictionary<,>` consumers, `FrozenDictionary`-style build-once lookups). Sits between the Quick start and Benchmarks sections so a reader who has scanned the API surface can pick the right type without spelunking `docs/api/`. Implements the "Document when to use which collection" item from issue #15.
diff --git a/src/Celerity.Tests/Collections/ContainsValueTests.cs b/src/Celerity.Tests/Collections/ContainsValueTests.cs
new file mode 100644
index 0000000..a42159a
--- /dev/null
+++ b/src/Celerity.Tests/Collections/ContainsValueTests.cs
@@ -0,0 +1,288 @@
+using Celerity.Collections;
+using Celerity.Hashing;
+
+namespace Celerity.Tests.Collections;
+
+public class ContainsValueTests
+{
+    // ---------------- IntDictionary ----------------
+
+    [Fact]
+    public void IntDictionary_EmptyMap_ReturnsFalse()
+    {
+        var map = new IntDictionary<int>();
+        Assert.False(map.ContainsValue(0));
+        Assert.False(map.ContainsValue(42));
+    }
+
+    [Fact]
+    public void IntDictionary_FindsValueInRegularSlot()
+    {
+        var map = new IntDictionary<int> { [1] = 100, [2] = 200, [3] = 300 };
+        Assert.True(map.ContainsValue(200));
+    }
+
+    [Fact]
+    public void IntDictionary_ReturnsFalseForMissingValue()
+    {
+        var map = new IntDictionary<int> { [1] = 100, [2] = 200 };
+        Assert.False(map.ContainsValue(999));
+    }
+
+    [Fact]
+    public void IntDictionary_FindsValueOnlyInZeroKeySlot()
+    {
+        var map = new IntDictionary<int>();
+        map[0] = 777;
+        Assert.True(map.ContainsValue(777));
+    }
+
+    [Fact]
+    public void IntDictionary_DefaultValueLookup_ZeroValue()
+    {
+        // After insert, value 0 must be reachable via ContainsValue.
+        var map = new IntDictionary<int> { [5] = 0, [6] = 1 };
+        Assert.True(map.ContainsValue(0));
+
+        // But an empty dictionary must NOT report 0 — the EMPTY_KEY slots
+        // are filled with default(TValue) and must be skipped by the scan.
+        var empty = new IntDictionary<int>();
+        Assert.False(empty.ContainsValue(0));
+    }
+
+    [Fact]
+    public void IntDictionary_DefaultValueLookup_OnlyZeroKeyHasDefaultValue()
+    {
+        // Same trap as above but with the value sitting only in the
+        // out-of-band zero-key slot.
+        var map = new IntDictionary<int>();
+        map[0] = 0;
+        Assert.True(map.ContainsValue(0));
+    }
+
+    [Fact]
+    public void IntDictionary_NullValueLookup_ReferenceType()
+    {
+        var map = new IntDictionary<string>();
+        map[1] = "one";
+        map[2] = null;
+        Assert.True(map.ContainsValue(null));
+
+        var noNulls = new IntDictionary<string> { [1] = "one", [2] = "two" };
+        Assert.False(noNulls.ContainsValue(null));
+    }
+
+    [Fact]
+    public void IntDictionary_DuplicateValues_ReturnsTrue()
+    {
+        var map = new IntDictionary<int>
+        {
+            [1] = 42,
+            [2] = 42,
+            [3] = 42,
+        };
+        Assert.True(map.ContainsValue(42));
+    }
+
+    [Fact]
+    public void IntDictionary_SurvivesResize()
+    {
+        var map = new IntDictionary<int>(capacity: 4);
+        for (int i = 1; i <= 100; i++)
+            map[i] = i * 10;
+
+        Assert.True(map.ContainsValue(770));
+        Assert.False(map.ContainsValue(-1));
+    }
+
+    [Fact]
+    public void IntDictionary_AfterRemove_ReturnsFalse()
+    {
+        var map = new IntDictionary<int> { [1] = 100, [2] = 200 };
+        map.Remove(1);
+        Assert.False(map.ContainsValue(100));
+        Assert.True(map.ContainsValue(200));
+    }
+
+    [Fact]
+    public void IntDictionary_AfterZeroKeyRemove_ReturnsFalse()
+    {
+        var map = new IntDictionary<int>();
+        map[0] = 555;
+        map[1] = 100;
+        map.Remove(0);
+        Assert.False(map.ContainsValue(555));
+        Assert.True(map.ContainsValue(100));
+    }
+
+    // ---------------- LongDictionary ----------------
+
+    [Fact]
+    public void LongDictionary_EmptyMap_ReturnsFalse()
+    {
+        var map = new LongDictionary<int>();
+        Assert.False(map.ContainsValue(0));
+        Assert.False(map.ContainsValue(42));
+    }
+
+    [Fact]
+    public void LongDictionary_FindsValueInRegularSlot()
+    {
+        var map = new LongDictionary<int> { [1L] = 100, [2L] = 200, [3L] = 300 };
+        Assert.True(map.ContainsValue(200));
+    }
+
+    [Fact]
+    public void LongDictionary_ReturnsFalseForMissingValue()
+    {
+        var map = new LongDictionary<int> { [1L] = 100, [2L] = 200 };
+        Assert.False(map.ContainsValue(999));
+    }
+
+    [Fact]
+    public void LongDictionary_FindsValueOnlyInZeroKeySlot()
+    {
+        var map = new LongDictionary<int>();
+        map[0L] = 777;
+        Assert.True(map.ContainsValue(777));
+    }
+
+    [Fact]
+    public void LongDictionary_DefaultValueLookup_ZeroValue()
+    {
+        var empty = new LongDictionary<int>();
+        Assert.False(empty.ContainsValue(0));
+
+        var map = new LongDictionary<int> { [5L] = 0, [6L] = 1 };
+        Assert.True(map.ContainsValue(0));
+    }
+
+    [Fact]
+    public void LongDictionary_NullValueLookup_ReferenceType()
+    {
+        var map = new LongDictionary<string>();
+        map[1L] = "one";
+        map[2L] = null;
+        Assert.True(map.ContainsValue(null));
+    }
+
+    [Fact]
+    public void LongDictionary_SurvivesResize()
+    {
+        var map = new LongDictionary<int>(capacity: 4);
+        for (long i = 1; i <= 100; i++)
+            map[i] = (int)(i * 10);
+
+        Assert.True(map.ContainsValue(770));
+        Assert.False(map.ContainsValue(-1));
+    }
+
+    // ---------------- CelerityDictionary ----------------
+
+    [Fact]
+    public void CelerityDictionary_EmptyMap_ReturnsFalse()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher>();
+        Assert.False(map.ContainsValue(0));
+        Assert.False(map.ContainsValue(42));
+    }
+
+    [Fact]
+    public void CelerityDictionary_FindsValueInRegularSlot()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher> { [1] = 100, [2] = 200, [3] = 300 };
+        Assert.True(map.ContainsValue(200));
+    }
+
+    [Fact]
+    public void CelerityDictionary_ReturnsFalseForMissingValue()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher> { [1] = 100, [2] = 200 };
+        Assert.False(map.ContainsValue(999));
+    }
+
+    [Fact]
+    public void CelerityDictionary_FindsValueOnlyInDefaultKeySlot_IntKey()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher>();
+        map[0] = 777;
+        Assert.True(map.ContainsValue(777));
+    }
+
+    [Fact]
+    public void CelerityDictionary_FindsValueOnlyInDefaultKeySlot_NullStringKey()
+    {
+        var map = new CelerityDictionary<string, int, StringFnV1AHasher>();
+        map[null!] = 777;
+        Assert.True(map.ContainsValue(777));
+    }
+
+    [Fact]
+    public void CelerityDictionary_DefaultValueLookup_ZeroValue()
+    {
+        // EMPTY_KEY slots in the probe array are populated with default(TKey)
+        // and default(TValue). ContainsValue must skip those.
+        var empty = new CelerityDictionary<int, int, Int32WangNaiveHasher>();
+        Assert.False(empty.ContainsValue(0));
+
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher> { [5] = 0, [6] = 1 };
+        Assert.True(map.ContainsValue(0));
+    }
+
+    [Fact]
+    public void CelerityDictionary_NullValueLookup_ReferenceType()
+    {
+        var map = new CelerityDictionary<int, string, Int32WangNaiveHasher>();
+        map[1] = "one";
+        map[2] = null;
+        Assert.True(map.ContainsValue(null));
+
+        var noNulls = new CelerityDictionary<int, string, Int32WangNaiveHasher> { [1] = "one", [2] = "two" };
+        Assert.False(noNulls.ContainsValue(null));
+    }
+
+    [Fact]
+    public void CelerityDictionary_DuplicateValues_ReturnsTrue()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher>
+        {
+            [1] = 42,
+            [2] = 42,
+            [3] = 42,
+        };
+        Assert.True(map.ContainsValue(42));
+    }
+
+    [Fact]
+    public void CelerityDictionary_SurvivesResize()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher>(capacity: 4);
+        for (int i = 1; i <= 100; i++)
+            map[i] = i * 10;
+
+        Assert.True(map.ContainsValue(770));
+        Assert.False(map.ContainsValue(-1));
+    }
+
+    [Fact]
+    public void CelerityDictionary_AfterDefaultKeyRemove_ReturnsFalse()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher>();
+        map[0] = 555;
+        map[1] = 100;
+        map.Remove(0);
+        Assert.False(map.ContainsValue(555));
+        Assert.True(map.ContainsValue(100));
+    }
+
+    [Fact]
+    public void CelerityDictionary_AfterClear_ReturnsFalse()
+    {
+        var map = new CelerityDictionary<int, int, Int32WangNaiveHasher> { [1] = 100, [2] = 200 };
+        map[0] = 300;
+        map.Clear();
+        Assert.False(map.ContainsValue(100));
+        Assert.False(map.ContainsValue(200));
+        Assert.False(map.ContainsValue(300));
+    }
+}
diff --git a/src/Celerity/Collections/CelerityDictionary.cs b/src/Celerity/Collections/CelerityDictionary.cs
index 757cae9..f523859 100644
--- a/src/Celerity/Collections/CelerityDictionary.cs
+++ b/src/Celerity/Collections/CelerityDictionary.cs
@@ -186,6 +186,42 @@ public bool ContainsKey(TKey key)
         return ProbeForKey(key) >= 0;
     }
 
+    /// <summary>
+    /// Determines whether the dictionary contains the specified value.
+    /// </summary>
+    /// <param name="value">
+    /// The value to locate. Equality is determined via
+    /// <see cref="EqualityComparer{T}.Default"/>, matching BCL
+    /// <see cref="Dictionary{TKey, TValue}.ContainsValue(TValue)"/> semantics.
+    /// </param>
+    /// <returns><c>true</c> if a matching value is found; otherwise, <c>false</c>.</returns>
+    /// <remarks>
+    /// This operation is <c>O(n)</c> in the dictionary's count: it scans the
+    /// probe table (skipping empty slots) and, when present, the out-of-band
+    /// default-key slot.
+    /// </remarks>
+    public bool ContainsValue(TValue? value)
+    {
+        var valueComparer = EqualityComparer<TValue?>.Default;
+
+        if (_hasDefaultKey && valueComparer.Equals(_defaultKeyValue, value))
+            return true;
+
+        var keyComparer = EqualityComparer<TKey>.Default;
+        TKey?[] keys = _keys;
+        TValue?[] values = _values;
+        for (int i = 0; i < keys.Length; i++)
+        {
+            if (!keyComparer.Equals(keys[i], default(TKey)) &&
+                valueComparer.Equals(values[i], value))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /// <summary>
     /// Attempts to get the value associated with the specified key.
     /// </summary>
diff --git a/src/Celerity/Collections/IntDictionary.cs b/src/Celerity/Collections/IntDictionary.cs
index 5a7a0da..0ceec9c 100644
--- a/src/Celerity/Collections/IntDictionary.cs
+++ b/src/Celerity/Collections/IntDictionary.cs
@@ -241,6 +241,38 @@ public bool ContainsKey(int key)
         return ProbeForKey(key) >= 0;
     }
 
+    /// <summary>
+    /// Determines whether the dictionary contains the specified value.
+    /// </summary>
+    /// <param name="value">
+    /// The value to locate. Equality is determined via
+    /// <see cref="EqualityComparer{T}.Default"/>, matching BCL
+    /// <see cref="Dictionary{TKey, TValue}.ContainsValue(TValue)"/> semantics.
+    /// </param>
+    /// <returns><c>true</c> if a matching value is found; otherwise, <c>false</c>.</returns>
+    /// <remarks>
+    /// This operation is <c>O(n)</c> in the dictionary's count: it scans the
+    /// probe table (skipping empty slots) and, when present, the out-of-band
+    /// zero-key slot.
+    /// </remarks>
+    public bool ContainsValue(TValue? value)
+    {
+        var comparer = EqualityComparer<TValue?>.Default;
+
+        if (_hasZeroKey && comparer.Equals(_zeroValue, value))
+            return true;
+
+        int[] keys = _keys;
+        TValue?[] values = _values;
+        for (int i = 0; i < keys.Length; i++)
+        {
+            if (keys[i] != EMPTY_KEY && comparer.Equals(values[i], value))
+                return true;
+        }
+
+        return false;
+    }
+
     /// <summary>
     /// Attempts to get the value associated with the specified key.
     /// </summary>
diff --git a/src/Celerity/Collections/LongDictionary.cs b/src/Celerity/Collections/LongDictionary.cs
index ee071e7..628ccd7 100644
--- a/src/Celerity/Collections/LongDictionary.cs
+++ b/src/Celerity/Collections/LongDictionary.cs
@@ -241,6 +241,38 @@ public bool ContainsKey(long key)
         return ProbeForKey(key) >= 0;
     }
 
+    /// <summary>
+    /// Determines whether the dictionary contains the specified value.
+    /// </summary>
+    /// <param name="value">
+    /// The value to locate. Equality is determined via
+    /// <see cref="EqualityComparer{T}.Default"/>, matching BCL
+    /// <see cref="Dictionary{TKey, TValue}.ContainsValue(TValue)"/> semantics.
+    /// </param>
+    /// <returns><c>true</c> if a matching value is found; otherwise, <c>false</c>.</returns>
+    /// <remarks>
+    /// This operation is <c>O(n)</c> in the dictionary's count: it scans the
+    /// probe table (skipping empty slots) and, when present, the out-of-band
+    /// zero-key slot.
+    /// </remarks>
+    public bool ContainsValue(TValue? value)
+    {
+        var comparer = EqualityComparer<TValue?>.Default;
+
+        if (_hasZeroKey && comparer.Equals(_zeroValue, value))
+            return true;
+
+        long[] keys = _keys;
+        TValue?[] values = _values;
+        for (int i = 0; i < keys.Length; i++)
+        {
+            if (keys[i] != EMPTY_KEY && comparer.Equals(values[i], value))
+                return true;
+        }
+
+        return false;
+    }
+
     /// <summary>
     /// Attempts to get the value associated with the specified key.
     /// </summary>