There is growing interest in research and practice in examining the diverse forms of crowdsourcing - from clickwork to highly specialized creative and innovation tasks - from the perspective of crowdworkers. This research project contributes to a crowdworker-centered understanding. The focus of the project is on the participation possibilities of crowdworkers, in distinction to the legally defined co-determination, understood as non-legally anchored, voluntarily initiated forms of influence by platforms on questions regarding work and utilization processes. This focus is taken into account by answering the following research questions: (How) do crowdsourcing platforms organize participation opportunities for crowdworkers so far? What does an ideal participation model look like? How compatible is this approach with legally anchored co-determination instruments? The project pursues the following goals: First, crowdsourcing intermediaries (platforms) from different categories (see Leimeister et al., 2016) are examined with regard to their forms of participation. Second, based on this empirical comparative study as well as a comprehensive literature review, a scenario for ideal-typical participation models for different types of crowdsourcing platforms is developed. Third, this scenario is extended by checking its compatibility with legally anchored participation models.