This chapter addresses the representation of people’s presence and behavior in building performance simulation. The subject of people in building performance simulation can be approached from a number of distinct vantage points. Simulation tools are of course developed and used by people. Specific building simulation use cases may require individuals’ presence states as input information, while they do not necessarily require randomly generated non-repeating occupancy state profiles. In building performance models, non-adaptive occupant actions can be simply represented by schedules. Thereby, the assumption is that the time of the day, day of the week, or the month of the year can be used to make assumptions regarding occupant behavior. Performance simulation models can assume different levels of resolution with regard to the representation of the underlying (physical) phenomena, required (input) information, and produced results (output).