Crowdsourcing can be an effective way for cultural heritage institutions to engage the public by having them help with labor-intensive tasks like transcription. Examples where this has worked well include contributions to the Oxford English Dictionary, Wikipedia, transcription of over 47 million lines from Australian newspapers by local and family historians, and collection of over 1.5 million bird observations in one month by the eBird project. For crowdsourcing to be sustainable, interfaces need to be engaging; contributors need recognition; and crowdsourcing should be seen as part of a broader public engagement mission rather than just a single project.