The study deals with syntactic and formal features of interrogative utterances, illocutionary and dialogic aspects of interrogative acts, and the lexical/semantic analysis of interrogative verbs. Detailed descriptions are made of sequence-dependent interrogative acts such as 'ask back', 'inquire', 'question', 'counter-question', and 'query'. The lexical/semantic analysis delineates the uses of the verbs fragen (ask), zurückfragen (ask back), nachfragen (inquire), and hinterfragen (query), and establishes the connections with the corresponding types of interrogative. The study is based on an extensive corpus.