This chapter presents erotetic calculi for classical logic—both propositional and first-order. As explained in the first chapter, erotetic calculi are systems that transform questions of certain formal languages. The intuitive interpretation underlying this formalism is that the aim of such transformations is to solve the problem expressed by the initial question. Thus, the entire process of transforming one question into further questions can be viewed as a model of question processing, understood as a cognitive, problem-solving activity. In the previous chapter, we also referred to this process as inquiring, and we completed the picture by comparing this process against that of justifying, where the latter can be seen as the intuitive counterpart of a proof in more traditional proof systems, such as axiomatic systems, sequent systems, or natural deduction systems.