In the process reflecting citizen science and its practices, many questions arise.How old is citizen science? What is the difference, if any, between citizen science,participatory science, post-normal science, civic science, and crowd science? Iscitizen science just a new political term in order to obtain funding? Some criticsview citizen science as a renewed neoliberal approach to exploit citizens by makingthem work for free when data is a key asset of our century. These questions may notbe fully answerable, but they surely deserve considered debate. These questions are aprime example of the need to maintain a lively discourse around citizen science, withas many practitioners as possible, and then bring together in a single book all theseperspectives. Therefore, the present volume aims to offer to those who are new to thefield of citizen science an overview of the different aspects of citizen science and thecurrent developments and discussions in thefield. The large number of chapters is anillustration of how diverse the citizen science world is and how many differentaspects need to be considered when delving into the field.