This chapter is about the design of corpora and types of corpora. Changes in the concept of a corpus are discussed, in particular the provision of metadata to allow personalised sub-corpora to be compiled on an ad hoc basis from a large corpus. The design features of size, balance, representativeness and comparability are discussed, with an emphasis on the constraints imposed by practical concerns. These types of corpora are explained: general or reference, specialised corpus, diachronic, monitor, learner, pedagogic, multilingual (parallel and comparable) and multimodal. Specific issues involved in compiling corpora from particular sources are discussed. The chapter includes a list of corpora that are referred to frequently in the rest of the book.