Everyone wins or nobody does. Cooperative games put players on the same side against a shared problem, whether that is spreading disease, dungeon monsters, or a ticking clock. The real design challenge is creating genuine difficulty without letting one player solve the puzzle for everyone else. Good cooperative games force meaningful choices under pressure, where the right answer is not obvious and the group has to argue its way to a decision. Pandemic made the format mainstream; Spirit Island took it into heavier territory; Hanabi proved it could work in fifteen minutes with a deck of cards.