Crowdsourcing has been studied in a variety of domains, which makes the body of knowledge hard to be organised. To help readers understand key aspects of crowdsourcing and provide organised foundation for the book, this chapter presents a focused literature review of crowdsourcing research. The review covers three major strands. The first strand examines the conceptualisation of crowdsourcing. It shows main pillars behind crowdsourcing and provides a definition of the concept. The second strand reviews basic classifications in the crowdsourcing domain: applications, tasks, members, and platforms, which are essential for exploring crowdsourcing processes. The last strand assesses the current state of crowdsourcing processes and business process crowdsourcing. It shows that business process crowdsourcing is important to establish repeatable crowdsourcing processes. It also shows that the domain is still in an early state with a small amount of related literature, which needs to be further conceptualised, structured, and supported.