In order to create rhetorically effective and engaging pieces, research writers must be able to find appropriate and diverse sources and to evaluate those sources for usefulness and credibility. This chapter discusses how to locate such sources and how to evaluate them. On the one hand, this is a chapter about the nuts and bolts of research. If you have written research papers before, searching for sources and citing them in your paper may, at times, have appeared to you as purely mechanical processes, chores necessary to produce a paper. On the other hand, when writers work with research sources, first finding and then evaluating them, they do rhetorical work. Finding good sources and using them effectively helps you to create a message and a persona which your readers are more likely to accept, believe, and be interested in than if unsuitable and unreliable sources are used. This chapter covers the various kinds of research sources available to writers. It discusses how to find, evaluate, and use primary and secondary sources, printed and online ones.