Citizen science has become more popular in recent years, quickly taking on a variety of potentially conflicting characteristics: a way to collect massive data sets at relatively low cost, a way to break science out of the ivory tower and better engage the public, an approach to educate lay people in scientific methods. But the extent of current citizen science practice-the types of actors and scientific disciplines who take part-is still poorly understood. This article builds on recent surveys of citizen science in PLOS One by analyzing citizen science practice in Germany and Austria through the projects on two online platforms. We find evidence supporting previous findings that citizen science is a phenomenon strongest in biodiversity and environmental monitoring research, but at home in a number of scientific fields, such as history and geography. In addition, our survey method yields new insights into citizen science projects initiated by non-scientific actors. We close by discussing additional methodological considerations in attempting to present a cross-disciplinary overview of citizen science.