So you’re interested in working with data produced by other people. Awesome! There are lots of data out there, waiting to be reused, combined with other datasets, or used differently. Some people refer to this as secondary data analysis. This approach can be a great way to expand the scope of your research, answer questions at a bigger spatial or temporal scale, gain insights into how other systems work, test your ideas in different places, and build collaborations. This primer is designed to help get you started.