Computers are now widely used in the preparation of dictionaries. There are many advantages in maintaining and updating a dictionary in electronic form, most obviously that printed versions can be typeset directly from the electronic copy. But more than that, electronic dictionaries are beginning to be used by computers in retrieval systems. This chapter looks at electronic dictionaries and examines how lexical databases can help to refine and improve retrieval and analysis programs. It also traces the development of the uses of computers and dictionaries, and assesses various types of resources. Much research still needs to be done on the structure and contents of lexical and linguistic databases, especially for the semantic component, but the examples discussed in this chapter give some idea of the potential.