Many research methods enable a "snapshot in time" view into the user experience, whether it's a usability test of the first-encounter experience or a post-transaction satisfaction survey. People's interactions with and attitudes toward products and services, however, change over time. Longitudinal research involves collecting data from the same group of people at multiple points in time. Increasingly, online technologies are making it possible to conduct longitudinal studies that are scalable for researchers and engaging for participants. This talk will touch on a few case studies and best practices for conducting online longitudinal studies.