When analyzing situations in which multiple people are experiencing emotions together – whether the emotions are positive or negative, and whether the situations are online or offline – we are intuitively drawn to the emotions of each individual in the situation. However, this type of analysis often seems incomplete. In many of the cases in which people experience emotions together, there appear to be emergent macro-level affective processes that cannot be readily captured at the individual level. This paper examines these macro-level affective phenomena, termed collective emotions. We open with a general review of research on collective psychological processes. We then define collective emotions and discuss their key features. Next, we focus our attention on the emergent properties of collective emotions and map them using three dimensions: quality, magnitude, and time course. Finally, we discuss pressing open questions and future directions.