diff --git a/2021/13/go.mod b/2021/13/go.mod
new file mode 100644
index 0000000..46e8376
--- /dev/null
+++ b/2021/13/go.mod
@@ -0,0 +1,9 @@
+module AoC/2021/13
+
+require AoC/2021/common v0.0.0
+
+require github.com/joho/godotenv v1.4.0 // indirect
+
+replace AoC/2021/common v0.0.0 => ../common
+
+go 1.17
diff --git a/2021/13/go.sum b/2021/13/go.sum
new file mode 100644
index 0000000..8c9f290
--- /dev/null
+++ b/2021/13/go.sum
@@ -0,0 +1,2 @@
+github.com/joho/godotenv v1.4.0 h1:3l4+N6zfMWnkbPEXKng2o2/MR5mSwTrBih4ZEkkz1lg=
+github.com/joho/godotenv v1.4.0/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
diff --git a/2021/13/main.go b/2021/13/main.go
new file mode 100644
index 0000000..bd9864d
--- /dev/null
+++ b/2021/13/main.go
@@ -0,0 +1,159 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type coordinate struct {
+	x int;
+	y int;
+}
+
+func printGrid(grid [][]bool) {
+	// Print grind
+	for _, line := range grid {
+		for _, pos := range line {
+			if pos {
+				fmt.Print("#")
+			} else {
+				fmt.Print(".")
+			}
+		}
+		fmt.Print("\n")
+	}
+}
+
+func fold(input *bufio.Scanner, once bool) int {
+	height := 0
+	width := 0
+
+	var coords []coordinate
+
+	// Construct initial grid
+	for input.Scan() {
+		line := input.Text()
+		if len(line) == 0 {
+			break
+		}
+
+		c := strings.Split(line, ",")
+
+		x, _ := strconv.Atoi(c[0])
+		y, _ := strconv.Atoi(c[1])
+
+		if x+1 > width {
+			width = x+1
+		}
+
+		if y+1 > height {
+			height = y+1
+		}
+
+		coords = append(coords, coordinate{x,y})
+	}
+
+	grid := make([][]bool, height)
+	for i := range grid {
+		grid[i] = make([]bool, width)
+	}
+
+	for _, c := range coords {
+		grid[c.y][c.x] = true
+	}
+
+	// printGrid(grid)
+
+	// Fold grid
+	for input.Scan() {
+		line := input.Text()
+
+		fmt.Println("Fold", line)
+		instruction := strings.Split(strings.Split(line, " ")[2], "=")
+
+		axis, _ := strconv.Atoi(instruction[1])
+
+		switch instruction[0] {
+		case "x":
+			fmt.Printf("vertical fold along %d\n", axis)
+			for y := range grid {
+				for x := 1; x <= axis; x++ {
+					grid[y][axis-x] = grid[y][axis-x] || grid[y][axis+x]
+					grid[y][axis+x] = false
+				}
+
+				grid[y] = grid[y][:axis]
+			}
+
+		case "y":
+			fmt.Printf("horizontal fold along %d\n", axis)
+			for y := 1; y <= axis; y++ {
+				for x := range grid[y] {
+					grid[axis-y][x] = grid[axis-y][x] || grid[axis+y][x]
+					grid[axis+y][x] = false
+				}
+			}
+
+			grid = grid[:axis]
+		}
+
+		// We only do the first instruction
+		if once {
+			break
+		}
+	}
+
+	// For part two the grid forms 8 letters
+	if !once {
+		printGrid(grid)
+	}
+
+	// Count dots
+	sum := 0
+	for y := range grid {
+		for x := range grid[y] {
+			if grid[y][x] {
+				sum++
+			}
+		}
+	}
+
+	return sum
+}
+
+func main() {
+	challenge := aoc.New(2021, 13)
+
+	challenge.Test(`6,10
+0,14
+9,10
+0,3
+10,4
+4,11
+6,0
+6,12
+4,1
+0,13
+10,12
+3,4
+3,0
+8,4
+1,10
+2,14
+8,10
+9,0
+
+fold along y=7
+fold along x=5`, []int{17, 16})
+
+	challenge.Solution(1, func (input *bufio.Scanner) int {
+		return fold(input, true)
+	})
+
+	challenge.Solution(2, func (input *bufio.Scanner) int {
+		return fold(input, false)
+	})
+}