Multi-winner voting is a way to select a subset of candidates, rather than just one, in a single election process. It is easy to carry out, and has become common, but its properties are not well understood. Because the voter must use a single ballot to indicate his or her preferences over all of the candidates, many nuances of preference are difficult or impossible to express. Many forms of ballot have been proposed for multi-winner voting; for some of them, there are multiple ways to determine the winning subset from a set of submitted ballots. Generally, these counting procedures balance two objectives - to elect only candidates who are well-supported individually, and to elect a subset of candidates with broad support. The breadth of multi-winner ballots and counting procedures is surveyed, and some properties that are desirable in multi-winner voting are described.