The web-based platform InnoCentive makes it possible for an organisation to broadcast a scientific problem in the form of a contest to a network of potential problem solvers who individually attempt to find a solution. InnoCentive is a so-called crowdsourcing platform. In a nutshell, crowdsourcing can be understood as organisations using web-based platforms, which are often managed by intermediaries, to call for ex ante unidentified, ideally large and diverse sets of individuals (the crowd) to solve problems identified and defined by the organisations. The first part of the book gives an overview on crowdsourcing by discussing basic tenets of crowdsourcing, different crowdsourcing types as well as the aggregation and selection mechanisms in crowdsourcing. In the second part, the focus lies on the contest model in crowdsourcing. Drawing an analogy from the brainstorming literature, I examine the role of the accessibility of peer contributions in contests. One conclusion is that an avenue for future research is hybrids, which combine different actors, group structures and aggregation, and selection mechanisms in the crowdsourcing process.