diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4eed9b7..6e1f6c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,10 +28,16 @@
 - X10D: Added `PointF.ToSizeF()`
 - X10D: Added `PointF.ToVector2()` for .NET < 6
 - X10D: Added `PopCount()` for built-in integer types
+- X10D: Added `ReadOnlySpan<char>.CountSubstring(char)`
+- X10D: Added `ReadOnlySpan<char>.CountSubstring(ReadOnlySpan<char>[, StringComparison])`
 - X10D: Added `RoundUpToPowerOf2()` for built-in integer types
 - X10D: Added `Size.ToPoint()`
 - X10D: Added `Size.ToPointF()`
 - X10D: Added `Size.ToVector2()`
+- X10D: Added `Span<char>.CountSubstring(char)`
+- X10D: Added `Span<char>.CountSubstring(Span<char>[, StringComparison])`
+- X10D: Added `string.CountSubstring(char)`
+- X10D: Added `string.CountSubstring(string[, StringComparison])`
 - X10D: Added `Quaternion.Multiply(Vector3)` - this functions as an equivalent to Unity's `Quaternion * Vector3` operator
 - X10D: Added `Vector2.Deconstruct()`
 - X10D: Added `Vector2.IsOnLine(LineF)`, `Vector2.IsOnLine(PointF, PointF)`, and `Vector2.IsOnLine(Vector2, Vector2)`
diff --git a/X10D.Tests/src/Text/StringTests.cs b/X10D.Tests/src/Text/StringTests.cs
index fa99f40..384c8b8 100644
--- a/X10D.Tests/src/Text/StringTests.cs
+++ b/X10D.Tests/src/Text/StringTests.cs
@@ -101,6 +101,55 @@ public class StringTests
         Assert.ThrowsException<ArgumentNullException>(() => "Hello World".ChangeEncoding(Encoding.UTF8, null!));
     }
 
+    [TestMethod]
+    public void CountSubstring_ShouldHonor_StringComparison()
+    {
+        Assert.AreEqual(0, "Hello World".CountSubstring('E'));
+        Assert.AreEqual(0, "Hello World".CountSubstring("E"));
+        Assert.AreEqual(1, "Hello World".CountSubstring("E", StringComparison.OrdinalIgnoreCase));
+        Assert.AreEqual(0, "Hello World".AsSpan().CountSubstring('E'));
+        Assert.AreEqual(1, "Hello World".AsSpan().CountSubstring("E".AsSpan(), StringComparison.OrdinalIgnoreCase));
+    }
+
+    [TestMethod]
+    public void CountSubstring_ShouldReturn0_GivenNoInstanceChar()
+    {
+        Assert.AreEqual(0, "Hello World".CountSubstring('z'));
+        Assert.AreEqual(0, "Hello World".CountSubstring("z"));
+        Assert.AreEqual(0, "Hello World".CountSubstring("z", StringComparison.OrdinalIgnoreCase));
+        Assert.AreEqual(0, "Hello World".AsSpan().CountSubstring('z'));
+        Assert.AreEqual(0, "Hello World".AsSpan().CountSubstring("z".AsSpan(), StringComparison.OrdinalIgnoreCase));
+    }
+
+    [TestMethod]
+    public void CountSubstring_ShouldReturn1_GivenSingleInstanceChar()
+    {
+        Assert.AreEqual(1, "Hello World".CountSubstring('e'));
+        Assert.AreEqual(1, "Hello World".CountSubstring("e"));
+        Assert.AreEqual(1, "Hello World".CountSubstring("e", StringComparison.OrdinalIgnoreCase));
+        Assert.AreEqual(1, "Hello World".AsSpan().CountSubstring('e'));
+        Assert.AreEqual(1, "Hello World".AsSpan().CountSubstring("e".AsSpan(), StringComparison.OrdinalIgnoreCase));
+    }
+
+    [TestMethod]
+    public void CountSubstring_ShouldReturn0_GivenEmptyHaystack()
+    {
+        Assert.AreEqual(0, string.Empty.CountSubstring('\0'));
+        Assert.AreEqual(0, string.Empty.CountSubstring(string.Empty));
+        Assert.AreEqual(0, string.Empty.CountSubstring(string.Empty, StringComparison.OrdinalIgnoreCase));
+        Assert.AreEqual(0, string.Empty.AsSpan().CountSubstring('\0'));
+        Assert.AreEqual(0, string.Empty.AsSpan().CountSubstring(string.Empty.AsSpan(), StringComparison.OrdinalIgnoreCase));
+    }
+
+    [TestMethod]
+    public void CountSubstring_ShouldThrow_GivenNullHaystack()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null!).CountSubstring('\0'));
+        Assert.ThrowsException<ArgumentNullException>(() => ((string?)null!).CountSubstring(string.Empty));
+        Assert.ThrowsException<ArgumentNullException>(() =>
+            ((string?)null!).CountSubstring(string.Empty, StringComparison.OrdinalIgnoreCase));
+    }
+
     [TestMethod]
     public void EnumParse_ShouldReturnCorrectValue_GivenString()
     {
diff --git a/X10D/src/Text/StringExtensions.cs b/X10D/src/Text/StringExtensions.cs
index b7ffa57..1eb544f 100644
--- a/X10D/src/Text/StringExtensions.cs
+++ b/X10D/src/Text/StringExtensions.cs
@@ -162,6 +162,159 @@ public static class StringExtensions
         return value.GetBytes(sourceEncoding).ToString(destinationEncoding);
     }
 
+    /// <summary>
+    ///     Counts the occurrences of a character within the current character span.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The character to count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this Span<char> haystack, char needle)
+    {
+        return CountSubstring((ReadOnlySpan<char>)haystack, needle);
+    }
+
+    /// <summary>
+    ///     Counts the occurrences of a character within the current character span.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The character to count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this ReadOnlySpan<char> haystack, char needle)
+    {
+        var count = 0;
+
+        for (var index = 0; index < haystack.Length; index++)
+        {
+            if (haystack[index] == needle)
+            {
+                count++;
+            }
+        }
+
+        return count;
+    }
+
+    /// <summary>
+    ///     Counts the occurrences of a character within the current string.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The character to count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this string haystack, char needle)
+    {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(haystack);
+#else
+        if (haystack is null)
+        {
+            throw new ArgumentNullException(nameof(haystack));
+        }
+#endif
+
+        return haystack.AsSpan().CountSubstring(needle);
+    }
+
+    /// <summary>
+    ///     Counts the occurrences of a substring within the current character span.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The character span to count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this ReadOnlySpan<char> haystack, ReadOnlySpan<char> needle)
+    {
+        return CountSubstring(haystack, needle, StringComparison.Ordinal);
+    }
+
+    /// <summary>
+    ///     Counts the occurrences of a substring within the current character span, using a specified string comparison method.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The character span to count.</param>
+    /// <param name="comparison">The string comparison method used for determining substring count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this ReadOnlySpan<char> haystack, ReadOnlySpan<char> needle, StringComparison comparison)
+    {
+        if (haystack.IsEmpty || needle.IsEmpty)
+        {
+            return 0;
+        }
+
+        int haystackLength = haystack.Length;
+        int needleLength = needle.Length;
+        var count = 0;
+
+        for (var index = 0; index < haystackLength - needleLength - 1; index++)
+        {
+            if (haystack[index..(index + needleLength)].Equals(needle, comparison))
+            {
+                count++;
+            }
+        }
+
+        return count;
+    }
+
+
+    /// <summary>
+    ///     Counts the occurrences of a substring within the current character span.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The character span to count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this Span<char> haystack, Span<char> needle)
+    {
+        return CountSubstring(haystack, needle, StringComparison.Ordinal);
+    }
+
+    /// <summary>
+    ///     Counts the occurrences of a substring within the current character span, using a specified string comparison method.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The character span to count.</param>
+    /// <param name="comparison">The string comparison method used for determining substring count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this Span<char> haystack, Span<char> needle, StringComparison comparison)
+    {
+        return CountSubstring((ReadOnlySpan<char>)haystack, needle, comparison);
+    }
+
+    /// <summary>
+    ///     Counts the occurrences of a substring within the current string.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The substring to count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this string haystack, string? needle)
+    {
+        return CountSubstring(haystack, needle, StringComparison.Ordinal);
+    }
+
+    /// <summary>
+    ///     Counts the occurrences of a substring within the current string, using a specified string comparison method.
+    /// </summary>
+    /// <param name="haystack">The haystack search space.</param>
+    /// <param name="needle">The substring to count.</param>
+    /// <param name="comparison">The string comparison method used for determining substring count.</param>
+    /// <returns>An integer representing the count of <paramref name="needle" /> inside <paramref name="haystack" />.</returns>
+    public static int CountSubstring(this string haystack, string? needle, StringComparison comparison)
+    {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(haystack);
+#else
+        if (haystack is null)
+        {
+            throw new ArgumentNullException(nameof(haystack));
+        }
+#endif
+
+        if (string.IsNullOrWhiteSpace(needle))
+        {
+            return 0;
+        }
+
+        return haystack.AsSpan().CountSubstring(needle, comparison);
+    }
+
     /// <summary>
     ///     Parses a <see cref="string" /> into an <see cref="Enum" />.
     /// </summary>