Mobile phone-based tools have the potential to revolutionize the way citizen scientists are recruited and retained, facilitating a new type of “connected” citizen scientist—one who collects scientifically relevant data as part of his or her daily routine. Established citizen science programs collect information at local, regional, and continental scales to help answer diverse questions in the geosciences and environmental sciences. Hundreds of thousands of citizen scientists contribute to recurring research projects such as the Audubon Society's annual Christmas Bird Count, which drew more than 60,000 observers in 2009, or the U.S. Environmental Protection Agency's Volunteer Monitoring program, through which trained volunteers improve the monitoring of water quality in lakes and streams across the United States. These programs have relied on traditional recruiting techniques and written observations. New methods for engaging participants through technology, specifically, mobile applications, or apps, provide unprecedented ways for participants to have immediate access to their own and others' observations and research results.