Citizen science programs are becoming increasingly popular among teachers, students, and families. The term "citizen scientist" has various definitions. It can refer to those who gather information for a particular science research study or to people who lobby for environmental protection for their communities. "Citizen science" has been called "community-centered science," "community science participatory community-action research," "street science," "traditional ecological knowledge, social justice, scientific literacy, and humanistic science education." This article provides numerous examples of citizen science projects that provide meaningful, authentic contexts for students to engage in the processes of science. These examples all include the task of collecting and sharing data with scientists and others. They cover a myriad of topics. Teachers can use these or others as part of a laboratory, field, or supplemental learning experience, or as an independent investigation. (Contains 1 figure and 7 online resources.)