Traditional information systems return answers after a user submits a complete query. Users often feel "left in the dark" when they have limited knowledge about the underlying data, and have to use a tryand-see approach for finding information. A recent trend of supporting autocompletion in these systems is a first step towards solving this problem. In this paper, we study a new information-access paradigm, called "search-as-you-type" or "type-ahead search," in which the system searches the underlying data on the fly as the user types in query keywords. It extends traditional prefix-based autocompletion interfaces by supporting full-text search on the data using tokenzied query keywords. We give an overview of this information-access paradigm, discuss research challenges and opportunities, and report recently developed techniques.