diff --git a/README.md b/README.md
index 62f0c01b..04039ed3 100644
--- a/README.md
+++ b/README.md
@@ -13,4 +13,4 @@ Development occurs in language-specific directories:
 |[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day6.kt)|[day6.py](py/aoc2023/day6.py)|[day6.rs](rs/src/day6.rs)|
 |[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day7.kt)|[day7.py](py/aoc2023/day7.py)|[day7.rs](rs/src/day7.rs)|
 |[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day8.kt)|[day8.py](py/aoc2023/day8.py)|[day8.rs](rs/src/day8.rs)|
-|[Day9.hs](hs/src/Day9.hs)|[Day9.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day9.kt)|[day9.py](py/aoc2023/day9.py)||
+|[Day9.hs](hs/src/Day9.hs)|[Day9.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day9.kt)|[day9.py](py/aoc2023/day9.py)|[day9.rs](rs/src/day9.rs)|
diff --git a/rs/benches/criterion.rs b/rs/benches/criterion.rs
index 5a66f55f..2304bc2c 100644
--- a/rs/benches/criterion.rs
+++ b/rs/benches/criterion.rs
@@ -1,4 +1,4 @@
-use aoc2023::{day1, day2, day3, day4, day5, day6, day7, day8};
+use aoc2023::{day1, day2, day3, day4, day5, day6, day7, day8, day9};
 use criterion::{black_box, Criterion};
 use std::env;
 use std::fs;
@@ -62,6 +62,12 @@ fn aoc2023_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day8::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(9)?;
+    let mut g = c.benchmark_group("day 9");
+    g.bench_function("part 1", |b| b.iter(|| day9::part1(black_box(&data))));
+    g.bench_function("part 2", |b| b.iter(|| day9::part2(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 
diff --git a/rs/src/day9.rs b/rs/src/day9.rs
new file mode 100644
index 00000000..b1040bad
--- /dev/null
+++ b/rs/src/day9.rs
@@ -0,0 +1,64 @@
+fn predict(nums: &[i32]) -> i32 {
+    if nums.iter().any(|&x| x != 0) {
+        nums.last().unwrap()
+            + predict(
+                &nums
+                    .iter()
+                    .zip(nums.iter().skip(1))
+                    .map(|(x, y)| y - x)
+                    .collect::<Vec<_>>(),
+            )
+    } else {
+        0
+    }
+}
+
+pub fn part1(data: &str) -> i32 {
+    data.lines()
+        .map(|line| {
+            predict(
+                &line
+                    .split_whitespace()
+                    .filter_map(|s| s.parse::<i32>().ok())
+                    .collect::<Vec<_>>(),
+            )
+        })
+        .sum()
+}
+
+pub fn part2(data: &str) -> i32 {
+    data.lines()
+        .map(|line| {
+            predict(
+                &line
+                    .split_whitespace()
+                    .rev()
+                    .filter_map(|s| s.parse::<i32>().ok())
+                    .collect::<Vec<_>>(),
+            )
+        })
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        0 3 6 9 12 15
+        1 3 6 10 15 21
+        10 13 16 21 30 45
+    "};
+
+    #[test]
+    fn part1_examples() {
+        assert_eq!(114, part1(EXAMPLE));
+    }
+
+    #[test]
+    fn part2_examples() {
+        assert_eq!(2, part2(EXAMPLE));
+    }
+}
diff --git a/rs/src/lib.rs b/rs/src/lib.rs
index 65fdb47f..b7940e51 100644
--- a/rs/src/lib.rs
+++ b/rs/src/lib.rs
@@ -6,3 +6,4 @@ pub mod day5;
 pub mod day6;
 pub mod day7;
 pub mod day8;
+pub mod day9;
diff --git a/rs/src/main.rs b/rs/src/main.rs
index 46711120..f7c3c2bf 100644
--- a/rs/src/main.rs
+++ b/rs/src/main.rs
@@ -1,4 +1,4 @@
-use aoc2023::{day1, day2, day3, day4, day5, day6, day7, day8};
+use aoc2023::{day1, day2, day3, day4, day5, day6, day7, day8, day9};
 use std::collections::HashSet;
 use std::env;
 use std::fs;
@@ -80,5 +80,13 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("9") {
+        let data = get_day_input(9)?;
+        println!("Day 9");
+        println!("{:?}", day9::part1(&data));
+        println!("{:?}", day9::part2(&data));
+        println!();
+    }
+
     Ok(())
 }