This chapter provides the definitions of surtitling and captioning for theatre and opera and examines the history of these practices. It analyzes the key features of surtitling in the opera, where surtitling originated as a service, and discusses theatre captioning, which enables productions to reach different types of audiences. According to M. Mateo, surtitling can be explored from a textual, ideological and technical perspective. The chapter discusses the textual, social and technical aspects of surtitling and captioning in these contexts. It explores the growing formal experimentation driven by technological advancements in the industry. For opera-goers, surtitles provide the translation needed to understand the text written originally in another language. Yvonne Griesel talks about three possible target audiences for interlingual surtitles. The three target audience are: source language audiences, target language audiences and audiences with knowledge of both source and target languages. The audience uses the surtitles for communicating with other symbolic modes used in the performance for creating meanings.