One significant obstacle improving the energy efficiency of buildings is a lack of understanding the occupant behavior in buildings. There is a need for systematic definitions to describe occupant behavior for different research purposes. To achieve this, three-levels of definitions for behavioral parameters for residential buildings were developed. The three levels - simple, intermediate and complex - serve three research purposes-statistical analysis, case studies and detailed diagnostics/simulation, respectively. For statistical analysis, a few parameters related to the schedule of occupancy and appliances are defined. More parameters are defined at the intermediate level, where definitions for the operation schedule and the set point of appliances for case studies are provided. For the complex level, subschemas are defined to describe the schedule, set points and control rules of three kinds of occupant behavior, namely occupancy, appliance operation, and window/shading operation. A statistical survey of occupant behavior in residential buildings in a city and a one-year monitoring of occupant behavior in a family were conducted to verify the simple-level definitions and the complex-level definitions. The result indicates the different levels of definitions can apply to different research purposes and reveals the main features and energy saving potential related to occupant behavior. (C) 2015 Elsevier B.V. All rights reserved.