Crowdsourcing is an emerging paradigm that promises to transform several domains: creative work, business work, cultural cooperation, etc. Crowdsourcing reflects the close-knit interplay between the latest computer technologies, the rapidly changing work model of the 21st century, and the very nature of people. The interplay makes for an exciting but at the same time challenging new field to investigate under the lens of a diverse set of disciplines, ranging from the technical to the social and from the theoretical to the applied. Early research has focused on an aspect of crowdsourcing known as micro-tasking. Micro-tasks are simple tasks (like image annotations) that anyone could perform. An