The definition and purpose of crowdsourcing and its relevance to libraries is discussed with particular reference to the Australian Newspapers service, FamilySearch, Wikipedia, Distributed Proofreaders, Galaxy Zoo and The Guardian MP's Expenses Scandal. These services have harnessed thousands of digital volunteers who transcribe, create, enhance and correct text, images and archives. Known facts about crowdsourcing are presented and helpful tips and strategies for libraries beginning to crowdsource are given.