diff --git a/README.md b/README.md
index 8f1863ed..eb867043 100644
--- a/README.md
+++ b/README.md
@@ -8,4 +8,4 @@ Development occurs in language-specific directories:
 |[Day1.hs](hs/src/Day1.hs)|[Day1.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day1.kt)|[day1.py](py/aoc2024/day1.py)|[day1.rs](rs/src/day1.rs)|
 |[Day2.hs](hs/src/Day2.hs)|[Day2.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day2.kt)|[day2.py](py/aoc2024/day2.py)|[day2.rs](rs/src/day2.rs)|
 |[Day3.hs](hs/src/Day3.hs)|[Day3.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day3.kt)|[day3.py](py/aoc2024/day3.py)|[day3.rs](rs/src/day3.rs)|
-|[Day4.hs](hs/src/Day4.hs)|[Day4.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day4.kt)|[day4.py](py/aoc2024/day4.py)||
+|[Day4.hs](hs/src/Day4.hs)|[Day4.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day4.kt)|[day4.py](py/aoc2024/day4.py)|[day4.rs](rs/src/day4.rs)|
diff --git a/rs/benches/criterion.rs b/rs/benches/criterion.rs
index 3a9e9b69..f1f0c49b 100644
--- a/rs/benches/criterion.rs
+++ b/rs/benches/criterion.rs
@@ -1,4 +1,4 @@
-use aoc2024::{day1, day2, day3};
+use aoc2024::{day1, day2, day3, day4};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -32,6 +32,12 @@ fn aoc2024_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day3::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(4)?;
+    let mut g = c.benchmark_group("day 4");
+    g.bench_function("part 1", |b| b.iter(|| day3::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day3::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 
diff --git a/rs/src/day4.rs b/rs/src/day4.rs
new file mode 100644
index 00000000..e32620cf
--- /dev/null
+++ b/rs/src/day4.rs
@@ -0,0 +1,78 @@
+use itertools::izip;
+
+pub fn part1(data: &str) -> usize {
+    let lines = data.lines().collect::<Vec<_>>();
+    let mut result = 0;
+    for (y, line) in lines.iter().enumerate() {
+        for x in 0..line.len() {
+            for dy in -1..=1 {
+                for dx in -1..=1 {
+                    if "XMAS".bytes().enumerate().all(|(i, b)| {
+                        y.checked_add_signed(i as isize * dy)
+                            .and_then(|y| lines.get(y))
+                            .and_then(|line| {
+                                x.checked_add_signed(i as isize * dx)
+                                    .and_then(|x| line.as_bytes().get(x))
+                            })
+                            == Some(&b)
+                    }) {
+                        result += 1;
+                    }
+                }
+            }
+        }
+    }
+    result
+}
+
+pub fn part2(data: &str) -> usize {
+    let lines = data.lines().collect::<Vec<_>>();
+    let mut result = 0;
+    for (above, line, below) in izip!(&lines[..], &lines[1..], &lines[2..]) {
+        for (nw, ne, b, sw, se) in izip!(
+            above.bytes(),
+            above.bytes().skip(2),
+            line.bytes().skip(1),
+            below.bytes(),
+            below.bytes().skip(2)
+        ) {
+            if b == b'A'
+                && (nw == b'M' && se == b'S' || se == b'M' && nw == b'S')
+                && (ne == b'M' && sw == b'S' || sw == b'M' && ne == b'S')
+            {
+                result += 1;
+            }
+        }
+    }
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        MMMSXXMASM
+        MSAMXMSMSA
+        AMXSXMAAMM
+        MSAMASMSMX
+        XMASAMXAMM
+        XXAMMXXAMA
+        SMSMSASXSS
+        SAXAMASAAA
+        MAMMMXMMMM
+        MXMXAXMASX
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(18, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(9, part2(EXAMPLE));
+    }
+}
diff --git a/rs/src/lib.rs b/rs/src/lib.rs
index 4e7d7123..5415e923 100644
--- a/rs/src/lib.rs
+++ b/rs/src/lib.rs
@@ -1,3 +1,4 @@
 pub mod day1;
 pub mod day2;
 pub mod day3;
+pub mod day4;
diff --git a/rs/src/main.rs b/rs/src/main.rs
index 2253ab6f..99a57c3b 100644
--- a/rs/src/main.rs
+++ b/rs/src/main.rs
@@ -1,4 +1,4 @@
-use aoc2024::{day1, day2, day3};
+use aoc2024::{day1, day2, day3, day4};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -40,5 +40,13 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("4") {
+        println!("Day 4");
+        let data = get_day_input(4)?;
+        println!("{:?}", day4::part1(&data));
+        println!("{:?}", day4::part2(&data));
+        println!();
+    }
+
     Ok(())
 }