Past research has shown that natural ventilation can be used to satisfy upwards of 98% of the yearly cooling demand when utilized in the appropriate climate zone. Yet widespread implementation of natural ventilation has been limited in practice. This delay in market adoption is mainly due to lack of effective and reliable control. Historically, control of natural ventilation was left to the occupant (i.e. they are responsible for opening and closing their windows) because occupants are more readily satisfied when given control of the indoor environment. This strategy has been shown to be effective during summer months, but can lead to both over and under ventilation, as well as the associated unnecessary energy waste during the winter months. This research presents the development and evaluation of a model-based control algorithm for natural ventilation. The proposed controller is designed to modulate the operable windows based on ambient temperature, wind speed, wind direction, solar radiation, indoor temperature and other building characteristics to ensure adequate ventilation and thermal comfort throughout the year without the use of mechanical ventilation and cooling systems. A midrise student dormitory building, located in Portland OR, has been used to demonstrate the performance of the proposed controller. Simulation results show that the model-based controller is able to reduce under-ventilated hours to 6.2% of the summer season (June - September) and 2.5% of the winter (October - May) while preventing over-heating during 99% of the year. In addition, the model-based-controller reduces the yearly energy cost by 33% when compared to a conventional heat pump system. As a proactive control, model-based control has been used in a wide range of building control applications. This research serves as proof-of-concept that it can be used to control operable windows to provide adequate ventilation year-round without significantly affecting thermal comfort. The resulting control algorithm significantly improves the reliability of natural ventilation design and could lead to a wider adoption of natural ventilation in appropriate climate zones.