Every language has declarative sentences, and so using declaratives is ubiquitous human behaviour. The widespread nature of this use of language is owed to the indispensable role that the sentence type plays in our lives: we use declaratives to circulate information with others, especially information about events that are not readily observed, and we use declaratives as the catalyst to perform other actions like promising or warning. But how does one type of sentence allow us all to do so much?To answer this question, How We Do Things With Declaratives develops a new psychological approach. It begins by identifying the effects of using declaratives that happen at the level of conversation, and then pinpoints the psychological capacities responsible for these effects. The result is an interlevel, mechanistic explanation. At bottom, what we do with declaratives is owed to how a cascade of cognitive capacities^—^including event cognition, mindreading, and norm cognition^—^are put into motion. This approach is used to uniformly explain both standard uses of declarative sentences, as well as non-standard uses like performative and hedged declaratives.