This chapter introduces a neuroimaging approach that has become popular among scientists over the last decade and that now is starting to attain clinical uses. The technique is called resting-state functional connectivity (RSFC), and it typically utilizes functional magnetic resonance imaging (fMRI) scans collected from subjects at rest (i.e., doing nothing) in the scanner. This chapter covers how the data are collected, processed, and turned into measures of brain organization. Some preliminary clinical uses of RSFC are presented. The priority of the chapter is not to broadly survey the field but instead to help readers better understand and more critically assess studies using RSFC techniques.