Before the optimization and control of HVAC water system, some basic definition and principle must be figured out. This chapter provides a description of system configuration, models, and fundamental control in typical HVAC water systems. It establishes the relationship between component operating parameters and energy consumption to provide theoretical support for solving global optimization problems in subsequent steps. The models primarily focus on parallel component, including descriptions of the number of component operating units, chiller, chilled water pump, air handling unit, cooling water pump, and cooling tower. Meanwhile, some conventional methods of tracking setpoint are also presented.