This deliverable contains a literature review of citizen science- related topics, situates citizen science in a historical context, discusses various conceptualisations of citizen science, and analyses existing categorisations and typologies of citizen science activities. It then presents a scheme of how citizen science can be categorised and characterised according to a broad range of relevant dimensions which can be used in Work Packages 2, 3 and 4, but also in future research, as no single endeavour may be able to take them all into account. Furthermore, it includes a short overview of the conceptual models for computer analytics that will be presented with all required detail in D1.2. Citizen science activities, especially crowdsourcing, are nothing new, and so are not initiatives in public engagement in science. An introductory chapter puts citizen science into a historical context by critically analysing the claims some citizen science advocates make when referring to the origins of citizen science. Another chapter is dedicated to some prominent conceptualisations of citizen science, which are related to each other and critically assessed. The ongoing debates about terminology in citizen science and about defining citizen science in general are presented and their issues are analysed. Concepts of citizen science and terminology issues are closely linked to issues of typologies and categorisations. Since categorisations and typologies are elaborated to get an overview of what the various forms of citizen science, prominent categorisations and typologies of citizen science are critically evaluated in a chapter of its own. The literature review addresses issues of actual, potential and claimed benefits brought by citizen science for the science system, ethical and integrity issues, caveats and potential pitfalls. Issues of participation in citizen science that are discussed in this report include participation patterns (as far as they are known), demographic and gender aspects, and barriers, enablers, incentives and disincentives for scientists and volunteers participating in citizen science. The chapter on education and citizen science discusses aspects of informal and formal, school and after-school, and online education. Furthermore, the visibility of citizen science activities and economic aspects of citizen science such as potential cost benefits, as they are presented in scientific literature, are assessed. The empirical basis for all this is relatively thin because not many systematic studies have been carried out. To support Work Packages 2, 3 and 4, categorisations of citizen science activities were broken down into the Activities & Dimensions Grid of Citizen Science and a checklist for characteristics was developed that builds upon the explanation of citizen science in the Science with and for Society Work Programme 2018 - 2020. The chapter on conceptual models for computer analytics describes the role and context of computational analytics in CS Track, building blocks for computational representation and analytics, and the specific methods to be applied in Work Package 3.