diff --git a/assets/highlighting-tests/csharp.cs b/assets/highlighting-tests/csharp.cs
new file mode 100644
index 00000000000..07c920e4611
--- /dev/null
+++ b/assets/highlighting-tests/csharp.cs
@@ -0,0 +1,158 @@
+// Single-line comment
+/* Block comment
+   spanning multiple lines */
+
+#nullable enable
+#region Usings
+global using static System.Console;
+using System;
+using System.Collections.Generic;
+#endregion
+
+#if DEBUG
+#pragma warning disable CS1591
+#endif
+
+namespace Demo.App;
+
+// Numbers
+42;
+3.14;
+.5;
+10_000_000;
+1e10;
+1.5e-3;
+0xff;
+0xffu;
+0xffl;
+0xfful;
+0xFF;
+0XFF;
+0b1010;
+0B1010;
+42u;
+42U;
+42L;
+42UL;
+42ul;
+42Ul;
+42lu;
+3.14f;
+3.14d;
+3.14m;
+3.14M;
+-.5_0_1e3_0d;
+-.5_0_1E3_0D;
+
+// Constants
+true;
+false;
+null;
+
+// Strings and characters
+'a';
+'\n';
+"double quotes with escape: \" \n \t \\";
+$"double quotes with a value {1 + 1}";
+@"C:\Temp\file.txt";
+@"verbatim with ""escaped"" quotes";
+$@"interpolated verbatim {1}";
+@$"interpolated verbatim {1}";
+"""
+raw string literal
+""";
+
+[Obsolete("Use NewThing instead")]
+public sealed class Greeter
+{
+    private readonly string _name;
+
+    public Greeter(string name)
+    {
+        _name = name;
+    }
+
+    public string SayHello(int count = 3)
+    {
+        var list = new List<int> { 1, 2, 3 };
+        var pi = 3.14159;
+        var hex = 0xDEAD_BEEF;
+        return $"Hello {_name}, count={count}";
+    }
+}
+
+public record Person(string Name, int Age);
+
+class Animal
+{
+    private int _age;
+    public int Age { get => _age; init => _age = value; }
+    protected bool _isAlive;
+    public bool IsAlive => _isAlive;
+
+    public virtual void Speak() { }
+}
+
+class Dog : Animal
+{
+    private string _bark = "woof";
+
+    public override void Speak()
+    {
+        Console.WriteLine(_bark);
+    }
+}
+
+public static class Program
+{
+    public static int Main(string[] args)
+    {
+        // Control flow keywords
+        if (args.Length == 0)
+        {
+            return 1;
+        }
+        else if (args.Length > 10)
+        {
+            return 2;
+        }
+        else
+        {
+            for (int i = 0; i < 10; i++)
+            {
+                if (i == 5) continue;
+                if (i == 8) break;
+            }
+
+            foreach (var arg in args)
+            {
+                Console.WriteLine(arg);
+            }
+
+            while (false) { }
+            do { } while (true);
+
+            switch (args.Length)
+            {
+                case 1: break;
+                default: break;
+            }
+        }
+
+        try
+        {
+            throw new Exception("oops");
+        }
+        catch (Exception e) when (e is InvalidOperationException)
+        {
+        }
+        finally
+        {
+        }
+
+        var query = from a in args where a is not null orderby a select a;
+        var g = new Greeter(args[0]);
+        Console.WriteLine(g.SayHello());
+        return 0;
+    }
+}
diff --git a/crates/edit/src/buffer/mod.rs b/crates/edit/src/buffer/mod.rs
index 468eb6898f1..f5dde4adb03 100644
--- a/crates/edit/src/buffer/mod.rs
+++ b/crates/edit/src/buffer/mod.rs
@@ -2177,6 +2177,7 @@ impl TextBuffer {
                     HighlightKind::ConstantNumeric => Some(IndexedColor::BrightGreen),
                     HighlightKind::KeywordControl => Some(IndexedColor::BrightMagenta),
                     HighlightKind::KeywordOther => Some(IndexedColor::BrightBlue),
+                    HighlightKind::KeywordPreprocessor => Some(IndexedColor::BrightBlue),
                     HighlightKind::MarkupBold => None,
                     HighlightKind::MarkupChanged => Some(IndexedColor::BrightBlue),
                     HighlightKind::MarkupDeleted => Some(IndexedColor::BrightRed),
diff --git a/crates/lsh-bin/src/main.rs b/crates/lsh-bin/src/main.rs
index 68547c431d5..748483d9012 100644
--- a/crates/lsh-bin/src/main.rs
+++ b/crates/lsh-bin/src/main.rs
@@ -122,20 +122,23 @@ fn run_render(generator: lsh::compiler::Generator, path: &Path) -> anyhow::Resul
             "string" => "\x1b[91m",   // Bright Red
             "variable" => "\x1b[96m", // Bright Cyan
 
-            "constant.language" => "\x1b[94m",   // Bright Blue
-            "constant.numeric" => "\x1b[92m",    // Bright Green
-            "keyword.control" => "\x1b[95m",     // Bright Magenta
-            "keyword.other" => "\x1b[94m",       // Bright Blue
-            "markup.bold" => "\x1b[1m",          // Bold
-            "markup.changed" => "\x1b[94m",      // Bright Blue
-            "markup.deleted" => "\x1b[91m",      // Bright Red
-            "markup.heading" => "\x1b[94m",      // Bright Blue
-            "markup.inserted" => "\x1b[92m",     // Bright Green
-            "markup.italic" => "\x1b[3m",        // Italic
-            "markup.link" => "\x1b[4m",          // Underlined
-            "markup.list" => "\x1b[94m",         // Bright Blue
-            "markup.strikethrough" => "\x1b[9m", // Strikethrough
-            "meta.header" => "\x1b[94m",         // Bright Blue
+            "constant.language" => "\x1b[94m",    // Bright Blue
+            "constant.numeric" => "\x1b[92m",     // Bright Green
+            "keyword.control" => "\x1b[95m",      // Bright Magenta
+            "keyword.other" => "\x1b[94m",        // Bright Blue
+            "keyword.preprocessor" => "\x1b[94m", // Bright Blue
+            "markup.bold" => "\x1b[1m",           // Bold
+            "markup.changed" => "\x1b[94m",       // Bright Blue
+            "markup.deleted" => "\x1b[91m",       // Bright Red
+            "markup.heading" => "\x1b[94m",       // Bright Blue
+            "markup.inserted" => "\x1b[92m",      // Bright Green
+            "markup.italic" => "\x1b[3m",         // Italic
+            "markup.link" => "\x1b[4m",           // Underlined
+            "markup.list" => "\x1b[94m",          // Bright Blue
+            "markup.strikethrough" => "\x1b[9m",  // Strikethrough
+            "meta.header" => "\x1b[94m",          // Bright Blue
+            "storage.annotation" => "\x1b[36m",   // Cyan
+            "storage.type" => "\x1b[36m",         // Cyan
 
             _ => {
                 unknown_kinds.push(hk.identifier.to_string());
diff --git a/crates/lsh/definitions/csharp.lsh b/crates/lsh/definitions/csharp.lsh
new file mode 100644
index 00000000000..16e1d9b9bc1
--- /dev/null
+++ b/crates/lsh/definitions/csharp.lsh
@@ -0,0 +1,75 @@
+#[display_name = "C#"]
+#[path = "**/*.cs"]
+#[path = "**/*.csx"]
+pub fn csharp() {
+    // Preprocessor directives always occupy the entire line.
+    if /\s*#\s*(?:define|elif|else|endif|endregion|error|if|line|nullable|pragma|region|undef|warning)\>.*/ {
+        yield keyword.preprocessor;
+        return;
+    }
+
+    until /$/ {
+        yield other;
+
+        if /\/\/.*/ {
+            yield comment;
+        } else if /\/\*/ {
+            loop {
+                yield comment;
+                await input;
+                if /\*\// {
+                    yield comment;
+                    break;
+                }
+            }
+        } else if /\$*"""/ {
+            // Raw string literal. It has no escape sequences and may span lines.
+            loop {
+                yield string;
+                if /"""/ {
+                    yield string;
+                    break;
+                }
+                await input;
+            }
+        } else if /\$?@\$?"/ {
+            // Verbatim string. `""` is the only escape sequence and it may span lines.
+            loop {
+                yield string;
+                if /""/ {
+                    // Escaped quote
+                } else if /"/ {
+                    yield string;
+                    break;
+                }
+                await input;
+            }
+        } else if /\$?"/ {
+            double_quote_string();
+        } else if /'/ {
+            single_quote_string();
+        } else if /\[([A-Z]\w*)/ {
+            yield $1 as storage.annotation;
+        } else if /(?:break|case|catch|continue|default|do|else|finally|foreach|for|goto|if|return|switch|throw|try|while|yield)\>/ {
+            yield keyword.control;
+        } else if /(?:abstract|and|async|as|await|base|checked|class|const|delegate|dynamic|enum|event|explicit|extern|file|fixed|from|get|global|group|implicit|init|interface|internal|into|in|is|join|let|lock|nameof|namespace|new|notnull|not|operator|orderby|or|out|override|params|partial|private|protected|public|readonly|record|ref|required|scoped|sealed|select|set|sizeof|stackalloc|static|struct|this|typeof|unchecked|unmanaged|unsafe|using|var|virtual|volatile|when|where|with)\>/ {
+            yield keyword.other;
+        } else if /(?:true|false|null)\>/ {
+            yield constant.language;
+        } else if /(?:bool|byte|char|decimal|double|float|int|long|nint|nuint|object|sbyte|short|string|uint|ulong|ushort|void)\>/ {
+            yield storage.type;
+        } else if /(?i:-?(?:0x[\da-f_]+|0b[01_]+|[\d_]+\.?[\d_]*|\.[\d_]+)(?:e[+-]?[\d_]+)?[dflmu]{0,2})/ {
+            if /\w+/ {
+                // Invalid numeric literal
+            } else {
+                yield constant.numeric;
+            }
+        } 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/src/compiler/charset.rs b/crates/lsh/src/compiler/charset.rs
index e7e301e3253..50529672301 100644
--- a/crates/lsh/src/compiler/charset.rs
+++ b/crates/lsh/src/compiler/charset.rs
@@ -100,6 +100,17 @@ impl Charset {
         }
     }
 
+    /// Adds the opposite case of every ASCII letter in the set.
+    pub fn fold_case(&mut self) {
+        for lower in b'a'..=b'z' {
+            let upper = lower.to_ascii_uppercase();
+            if self.get(lower) || self.get(upper) {
+                self.set(lower, true);
+                self.set(upper, true);
+            }
+        }
+    }
+
     pub fn is_superset_of(&self, other: &Charset) -> bool {
         for (&s, &o) in self.bits.iter().zip(other.bits.iter()) {
             // For self to be a superset, every bit in other must be in self
diff --git a/crates/lsh/src/compiler/regex.rs b/crates/lsh/src/compiler/regex.rs
index 9cc3370e25a..fba4206df0a 100644
--- a/crates/lsh/src/compiler/regex.rs
+++ b/crates/lsh/src/compiler/regex.rs
@@ -27,6 +27,7 @@
 //! | `foo`        | `Prefix("foo")` - single prefix check                    |
 //! | `\+\+\+`     | `Prefix("+++")` - escapes fused into literals            |
 //! | `(?i:foo)`   | `PrefixInsensitive("foo")`                               |
+//! | `(?i:[a-f])` | `Charset` with both cases folded in                      |
 //! | `[a-z]+`     | `Charset{cs, min=1, max=∞}` - greedy char class          |
 //! | `[a-z]?`     | `Charset{cs, min=0, max=1}` - optional char              |
 //! | `$`          | `EndOfLine` condition                                    |
@@ -441,6 +442,10 @@ impl<'a> RegexParser<'a> {
             }
         }
 
+        if self.case_insensitive {
+            charset.fold_case();
+        }
+
         if negated {
             charset.invert();
         }