Citizen science involves members of the public participating in scientific research projects in various ways. It can involve unpaid volunteers simply contributing data to projects, but may also allow for more extensive co-creation, where public groups participate in designing studies, methods, and analysis. Crowdsourcing utilizes the collective intelligence of large groups online to analyze large datasets or solve complex problems. Examples discussed include projects in neuroscience that use crowdsourcing to analyze brain images. The document outlines opportunities, challenges and definitions around different models of citizen science. It provides resources for those interested in learning more or getting involved in related projects and discussions.