diff --git a/assets/highlighting-tests/cs.cs b/assets/highlighting-tests/cs.cs
new file mode 100644
index 00000000000..cee84344a91
--- /dev/null
+++ b/assets/highlighting-tests/cs.cs
@@ -0,0 +1,151 @@
+// Comments
+// Single-line comment
+
+/*
+Multi-line
+comment
+*/
+
+global using static System.Console;
+using System;
+
+// Numbers
+42;
+3.14;
+.5;
+10_000_000;
+1e10;
+1.5e-3;
+0xff;
+0xffu;
+0xffl;
+0xfful;
+0xFF;
+0Xff;
+0XFF;
+0XFFU;
+0XFFL;
+0XFFLU;
+0b1010;
+0B1010;
+42u;
+42U;
+42l;
+42L;
+42UL;
+42Ul;
+42uL;
+42ul;
+42LU;
+42Lu;
+42lU;
+42lu;
+3.14f;
+3.14d;
+-.5_0_1e3_0d;
+
+// Constants
+true;
+false;
+null;
+
+// Strings and Characters
+'a';
+'\n';
+"double quotes with escape: \" \n \t \\";
+$"double quotes with a value {1 + 1}";
+@"double quotes with ";
+$@"";
+@$"";
+
+// Control flow keywords
+if (true)
+{
+
+}
+else if (false)
+{
+
+}
+else
+{
+
+}
+
+for (int i = 0; i < 10; i++)
+{
+    if (i == 5) continue;
+    if (i == 8) break;
+}
+
+while (false) { }
+do { } while (true);
+
+switch (42)
+{
+    case 1: break;
+    default: break;
+}
+
+try
+{
+    throw new Exception("oops");
+}
+catch (System.Exception)
+{
+
+}
+finally
+{
+
+}
+
+// Other keywords (some are contextually reserved)
+var a = 1;
+dynamic b = 2;
+T c = 3;
+
+string Greet(string name)
+{
+    return "Hello, " + name;
+}
+
+static int Factorial(int n)
+{
+    if (n == 0)
+    {
+        return 1;
+    }
+
+    return n * Factorial(n - 1);
+}
+
+class Animal
+{
+    private int _Age;
+    public int Age { get => _Age; }
+    protected bool _IsAlive;
+    public bool IsAlive { get => _IsAlive; }
+    public Animal(int age, bool isAlive)
+    {
+        _Age = age;
+        _IsAlive = isAlive;
+    }
+
+    public virtual void Speak() { }
+}
+
+class Dog : Animal
+{
+    private string _Bark;
+
+    public Dog(string bark, int age, bool isAlive) : base(age, isAlive)
+    {
+
+    }
+
+    public override void Speak()
+    {
+        Console.WriteLine(_Bark);
+    }
+}
diff --git a/assets/highlighting-tests/markdown.md b/assets/highlighting-tests/markdown.md
index 555b182f961..b0ecfbf1d1f 100644
--- a/assets/highlighting-tests/markdown.md
+++ b/assets/highlighting-tests/markdown.md
@@ -84,3 +84,10 @@ export function greet(name) {
 def greet(name: str) -> str:
     return f"hello {name}"
 ```
+
+```CSharp
+public string Greet(string name)
+{
+  return $"hello {name}";
+}
+```
diff --git a/crates/lsh/definitions/cs.lsh b/crates/lsh/definitions/cs.lsh
new file mode 100644
index 00000000000..18cd02f67be
--- /dev/null
+++ b/crates/lsh/definitions/cs.lsh
@@ -0,0 +1,60 @@
+#[display_name = "C#"]
+#[path = "**/*.cs"]
+pub fn CSharp() {
+    until /$/ {
+        yield other;
+
+        if /\/\/.*/ {
+            yield comment;
+        } else if /\/\*/ {
+            loop {
+                yield comment;
+                await input;
+                if /\*\// {
+                    yield comment;
+                    break;
+                }
+            }
+        } else if /[@$]{0,2}"/ {
+            until /$/ {
+                yield string;
+                if /\\./ {}
+                else if /"/ {
+                    yield string;
+                    break;
+                }
+                await input;
+            }
+        } else if /'/ {
+            until /$/ {
+                yield string;
+                if /\\./ {}
+                else if /'/ {
+                    yield string;
+                    break;
+                }
+                await input;
+            }
+        } else if /(?:global|using|static)/ {
+            yield keyword.control;
+        } else if /(?:as$|break|case|catch|checked|continue|default|do|else|for|foreach|finaly|fixed|goto|if|is$|lock|return|switch|throw|try|while|unchecked|by|descending|equals|extention|from|group|into|join|nameof|on$|or$|orderby|select|when|where|with|yield)/ {
+            yield keyword.control;
+        } else if /(?:abstract|bool|byte|char|class|const|decimal|delegate|double|enum|event|explicit|extern|float|implicit|int|interface|internal|long|namespace|new|object|operator|out|override|params|private|protected|public|readonly|ref|sealed|short|static|string|struct|this|typeof|uint|ulong|unsafe|ushort|virtual|void|volatile|add|args|async|await|dynamic|field|file|get|init|let|managed|nint|not|notnull|nuint|partial|record|required|sbyte|scoped|set|T|unmanaged|var)/ {
+            yield keyword.other;
+        } else if /(?i:-?(?i:0x[\da-fA-F_]+|0b[01_]+|[\d_]+\.?[\d_]*|\.[\d_]+)(?i:[+-]?[\d_]+|e[+-]?[\d_]+)?[uUlLfFdD]*)/ {
+            if /\w+/ {
+                // Invalid numeric literal
+            } else {
+                yield constant.numeric;
+            }
+        } else if /(?:true|false|null)/ {
+            yield constant.language;
+        }else if /(\w+)\s*\(/ {
+            yield $1 as method;
+        } else if /\w+/ {
+            // Gobble word chars to align the next iteration on a word boundary.
+        }
+
+        yield other;
+    }
+}
diff --git a/crates/lsh/definitions/markdown.lsh b/crates/lsh/definitions/markdown.lsh
index 77a005fe925..784c46e29cc 100644
--- a/crates/lsh/definitions/markdown.lsh
+++ b/crates/lsh/definitions/markdown.lsh
@@ -90,6 +90,16 @@ pub fn markdown() {
                     if /.*/ {}
                 }
             }
+        } else if /(?i:C\#|CSharp|cs)/ {
+            loop {
+                await input;
+                if /\s*```/ {
+                    return;
+                } else {
+                    CSharp();
+                    if /.*/ { }
+                }
+            }
         } else {
             loop {
                 await input;