A mechanism is like the rules of a game. We want to design the rules so that every player, even if they only care about themselves, ends up telling the truth. And they should want to tell the truth even if they have no clue what anyone else is doing. This chapter is about mechanisms where truth‑telling is not just a good idea—it’s the absolute best move a player can make, no matter what. That property is called dominant strategy incentive compatibility (DSIC), and it’s the gold standard for making a system that works no matter what.