diff --git a/Cargo.lock b/Cargo.lock
index 1e60d8b..f9f75a4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -15,9 +15,19 @@ dependencies = [
  "dotenvy",
  "indoc",
  "itertools",
+ "regex",
  "ureq",
 ]
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "base64"
 version = "0.22.1"
@@ -273,6 +283,12 @@ version = "0.4.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a7a70ba024b9dc04c27ea2f0c0548feb474ec5c54bba33a7f72f873a39d07b24"
 
+[[package]]
+name = "memchr"
+version = "2.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
+
 [[package]]
 name = "miniz_oxide"
 version = "0.8.0"
@@ -312,6 +328,35 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "regex"
+version = "1.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b544ef1b4eac5dc2db33ea63606ae9ffcfac26c1416a2806ae0bf5f56b201191"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "809e8dc61f6de73b46c85f4c96486310fe304c434cfa43669d7b40f711150908"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b15c43186be67a4fd63bee50d0303afffcef381492ebe2c5d87f324e1b8815c"
+
 [[package]]
 name = "ring"
 version = "0.17.8"
diff --git a/Cargo.toml b/Cargo.toml
index 35d95d8..4e9ccd4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,4 +7,5 @@ edition = "2021"
 dotenvy = "0.15.7"
 indoc = "2.0.5"
 itertools = "0.13.0"
+regex = "1.11.1"
 ureq = "2.11.0"
diff --git a/src/solutions/day_03.rs b/src/solutions/day_03.rs
new file mode 100644
index 0000000..8656418
--- /dev/null
+++ b/src/solutions/day_03.rs
@@ -0,0 +1,54 @@
+use itertools::Itertools;
+use regex::Regex;
+
+use crate::common::{Answer, Solution};
+
+pub struct Day03;
+
+impl Solution for Day03 {
+    fn name(&self) -> &'static str {
+        "Mull It Over"
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        let re = Regex::new(r"mul\((\d+),(\d+)\)").unwrap();
+
+        let sum = re
+            .captures_iter(input)
+            .map(|c| c.extract())
+            .map(|(_, [a, b])| a.parse::<u64>().unwrap() * b.parse::<u64>().unwrap())
+            .sum::<u64>();
+
+        Answer::Number(sum)
+    }
+
+    fn part_b(&self, input: &str) -> Answer {
+        let without_donts = input
+            .split("do()")
+            .map(|s| s.split_once("don't()").map(|(b, _)| b).unwrap_or(s))
+            .join("");
+
+        self.part_a(&without_donts)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::Day03;
+    use crate::common::Solution;
+
+    const INPUT_A: &str = "xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))";
+
+    const INPUT_B: &str =
+        "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))";
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day03.part_a(INPUT_A), 161.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day03.part_b(INPUT_B), 48.into());
+    }
+}
diff --git a/src/solutions/mod.rs b/src/solutions/mod.rs
index 3bc6a6a..f8c8bdb 100644
--- a/src/solutions/mod.rs
+++ b/src/solutions/mod.rs
@@ -2,5 +2,6 @@ use crate::common::Solution;
 
 mod day_01;
 mod day_02;
+mod day_03;
 
-pub const SOLUTIONS: &[&dyn Solution] = &[&day_01::Day01, &day_02::Day02];
+pub const SOLUTIONS: &[&dyn Solution] = &[&day_01::Day01, &day_02::Day02, &day_03::Day03];