diff --git a/2021/11/part1.mjs b/2021/11/part1.mjs
new file mode 100644
index 0000000..57b2926
--- /dev/null
+++ b/2021/11/part1.mjs
@@ -0,0 +1,68 @@
+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+export const processInput = (file) =>
+    fs.readFile(file, "utf8").then((content) =>
+        content
+            .split("\n")
+            .filter((x) => x)
+            .map((line) => line.split("").map((x) => parseInt(x)))
+    );
+
+export const genNeighbours = (maxX, maxY) => (x, y) =>
+    [
+        [-1, 0],
+        [1, 0],
+        [0, 1],
+        [0, -1],
+        [1, 1],
+        [-1, -1],
+        [1, -1],
+        [-1, 1],
+    ]
+        .map((delta) => _.zip(delta, [x, y]).map(_.sum))
+        .filter(([x, y]) => {
+            if (x < 0 || y < 0) return false;
+            if (x >= maxX || y >= maxY) return false;
+            return true;
+        });
+
+function powerUp(x, y, grid, toClear) {
+    grid[x][y]++;
+
+    if (grid[x][y] !== 10) return 0;
+
+    // FLASH!
+    toClear.push([x, y]);
+
+    return _.sum([
+        1,
+        ...genNeighbours(grid.length, grid[0].length)(x, y).map((coords) =>
+            powerUp(...coords, grid, toClear)
+        ),
+    ]);
+}
+
+export function playTurn(grid) {
+    let flashes = 0;
+    let toClear = [];
+
+    for (const x in grid) {
+        for (const y in grid[x]) {
+            flashes += powerUp(parseInt(x), parseInt(y), grid, toClear);
+        }
+    }
+
+    for (const [x, y] of toClear) {
+        grid[x][y] = 0;
+    }
+
+    return flashes;
+}
+
+export const printGrid = (grid) =>
+    grid.forEach((line) => console.log(line.join("")));
+
+export const solution = (grid) =>
+    _.sum(_.range(100).map(() => playTurn(grid)));
diff --git a/2021/11/part2.mjs b/2021/11/part2.mjs
new file mode 100644
index 0000000..a5329a9
--- /dev/null
+++ b/2021/11/part2.mjs
@@ -0,0 +1,19 @@
+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+import * as p1 from './part1.mjs';
+
+const allFlashed = grid => grid.every(
+        row => row.every( x => x === 0 )
+    );
+
+export function solution(grid) {
+    let step = 0;
+
+    while(true) {
+        step++;
+        p1.playTurn(grid);
+        if( allFlashed(grid) ) return step;
+    }
+}
diff --git a/2021/11/sample b/2021/11/sample
new file mode 100644
index 0000000..03743f6
--- /dev/null
+++ b/2021/11/sample
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
diff --git a/2021/11/test.mjs b/2021/11/test.mjs
new file mode 100644
index 0000000..dc33bdb
--- /dev/null
+++ b/2021/11/test.mjs
@@ -0,0 +1,23 @@
+// https://adventofcode.com/2021/day/11
+
+import tap from "tap";
+import fs from "fs-extra";
+
+import * as p1 from "./part1.mjs";
+import * as p2 from "./part2.mjs";
+
+
+tap.test("part1", async (t) => {
+    const sample = p1.processInput('sample');
+    const input = p1.processInput('input');
+
+    t.equal(p1.solution(await sample), 1656);
+    t.equal(p1.solution(await input), 1729);
+});
+
+tap.test("part2", async (t) => {
+    const sample = await p1.processInput('sample');
+    const input = await p1.processInput('input');
+    t.equal(p2.solution(sample), 195);
+    t.equal(p2.solution(input), 237);
+});