diff --git a/2021/4/go.mod b/2021/4/go.mod
new file mode 100644
index 0000000..4c58b8d
--- /dev/null
+++ b/2021/4/go.mod
@@ -0,0 +1,9 @@
+module AoC/2021/3
+
+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/2021/4/go.sum b/2021/4/go.sum
new file mode 100644
index 0000000..8c9f290
--- /dev/null
+++ b/2021/4/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/2021/4/main.go b/2021/4/main.go
new file mode 100644
index 0000000..86fb11d
--- /dev/null
+++ b/2021/4/main.go
@@ -0,0 +1,226 @@
+package main
+
+import (
+	"AoC/2021/common"
+	"bufio"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type Card struct {
+	numbers []int
+	row [5]int
+	column [5]int
+}
+
+func filter(in []string) []string {
+	n := 0
+	for _, s := range in {
+		if len(s) > 0 {
+			in[n] = s
+			n++
+		}
+	}
+	return in[:n]
+}
+
+func findWinner(numbers []int, cards []Card) (int, []int) {
+	for _, n := range numbers {
+		for j := range cards {
+			for k := range cards[j].numbers {
+				if cards[j].numbers[k] == n {
+
+					// Relpace the number to indicate is has been markeed
+					cards[j].numbers[k] = -1
+
+					row := k / 5
+					column := k % 5
+
+					cards[j].row[row]++
+					cards[j].column[column]++
+
+					if cards[j].row[row] == 5 || cards[j].column[column] == 5 {
+						return n, cards[j].numbers
+					}
+
+					break
+				}
+			}
+		}
+	}
+
+	fmt.Println("Failed to find a winner")
+
+	return -1, nil
+}
+
+func findLosing(numbers []int, cards []Card) (int, []int) {
+	for _, n := range numbers {
+		i := 0
+		for j := range cards {
+			hasWon := false
+			for k := range cards[j].numbers {
+				if cards[j].numbers[k] == n {
+
+					// Relpace the number to indicate is has been markeed
+					cards[j].numbers[k] = -1
+
+					row := k / 5
+					column := k % 5
+
+					cards[j].row[row]++
+					cards[j].column[column]++
+
+					if cards[j].row[row] == 5 || cards[j].column[column] == 5 {
+						hasWon = true
+						if len(cards) == 1 {
+							return n, cards[j].numbers
+						}
+					}
+				}
+			}
+			if !hasWon {
+				cards[i] = cards[j]
+				i++
+			}
+		}
+		cards = cards[:i]
+	}
+
+	fmt.Println("Failed to find a winner")
+
+	return -1, nil
+}
+
+func main() {
+	aoc := aoc.New(2021, 4)
+
+	aoc.Test(`
+7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7
+	`, []int{4512, 1924})
+
+	aoc.Solution(1, func (input *bufio.Scanner) int {
+		input.Scan()
+		line := input.Text()
+		var numbers []int
+		for _, num := range strings.Split(line, ",") {
+			n, err := strconv.Atoi(num)
+			if err != nil {
+				panic(err)
+			}
+
+			numbers = append(numbers, n)
+		}
+
+		var cards []Card
+		var rowNumber int
+		cardIndex := -1
+		for input.Scan() {
+			line = input.Text()
+
+			// A new line means that we start a new card
+			if len(line) == 0 {
+				card := Card{}
+				card.numbers = make([]int, 25)
+				cards = append(cards, card)
+				rowNumber = 0
+				cardIndex++
+			} else {
+				row := filter(strings.Split(line, " "))
+
+				for i, num := range row {
+					n, err :=  strconv.Atoi(num)
+					if err != nil {
+						panic(err)
+					}
+					cards[cardIndex].numbers[5*rowNumber + i] = n
+				}
+
+				rowNumber++
+			}
+		}
+
+		winning, unmarked := findWinner(numbers, cards)
+
+		sum := 0
+		for _, n  := range unmarked {
+			if n != -1 {
+				sum += n
+			}
+		}
+
+		return winning*sum
+	})
+
+	aoc.Solution(2, func (input *bufio.Scanner) int {
+		input.Scan()
+		line := input.Text()
+		var numbers []int
+		for _, num := range strings.Split(line, ",") {
+			n, err := strconv.Atoi(num)
+			if err != nil {
+				panic(err)
+			}
+
+			numbers = append(numbers, n)
+		}
+
+		var cards []Card
+		var rowNumber int
+		cardIndex := -1
+		for input.Scan() {
+			line = input.Text()
+
+			// A new line means that we start a new card
+			if len(line) == 0 {
+				card := Card{}
+				card.numbers = make([]int, 25)
+				cards = append(cards, card)
+				rowNumber = 0
+				cardIndex++
+			} else {
+				row := filter(strings.Split(line, " "))
+
+				for i, num := range row {
+					n, err :=  strconv.Atoi(num)
+					if err != nil {
+						panic(err)
+					}
+					cards[cardIndex].numbers[5*rowNumber + i] = n
+				}
+
+				rowNumber++
+			}
+		}
+
+		winning, unmarked := findLosing(numbers, cards)
+
+		sum := 0
+		for _, n  := range unmarked {
+			if n != -1 {
+				sum += n
+			}
+		}
+
+		return winning*sum
+	})
+}