Nanoemulsions exhibit unique behavior due to their nanoscopic dimensions, including remarkable droplet stability, interactions, and rheology. These properties are significantly enhanced by nanoscopic droplet size, as well as the selection of surfactant and other molecular species in solution. Electrostatic and polymer-induced interdroplet interactions are particularly powerful tools for fine-tuning the interdroplet interactions, and have led to stimuli-responsive nanoemulsion systems that provide deep insight into their unique properties. As such, nanoemulsions have emerged as powerful model systems for studying a number of colloidal phenomena including suspension rheology, repulsive and attractive colloidal glasses, aggregation processes, colloidal gelation and phase instability, and associative network formation in polymer–colloid mixtures. This review summarizes recent advances in understanding the colloidal behavior of nanoemulsions, and provides a unifying framework for understanding the various complex states that emerge, as well as perspective on emerging challenges and opportunities that will advance the use of nanoemulsions in both fundamental colloid science and technological applications. Display omitted •We review efforts to understand and control colloidal behavior of nanoemulsions.•Electrostatic and polymer-induced interdroplet interactions are discussed.•Repulsive interactions lead to jammed and compressed states at low volume fraction.•Attractive interactions lead to clustering, gelation, and colloidal phase separation.•Nanoemulsions are model fluids to study arrested states in colloidal dispersions.