Passive ventilation employs a set of strategies, potentially including building shape, internal configuration, orientation, aperture size and position, and microclimate design, to direct air through a building without the assistance of fans or pumps. Passive ventilation has received widespread attention in green building design, particularly in mild climates, because of its great potential to reduce cooling costs. The challenge of predicting airflow speed and direction within a building has encouraged development of sophisticated computational simulation tools, and the resulting confidence has, in turn, led to the design of passive and passive/mechanical hybrid ventilation systems in increasingly extreme climates. The Harm A. Weber Academic Center possesses one of the most ambitious hybrid ventilation systems in the world: in the hot continental climate of the midwestern United States, this building integrates passive and mechanical systems into a single network of airflow pathways. Aperture openings for the system are controlled automatically, using information provided by numerous internal and external sensors, such that the building can make use of multiple hybrid modes to utilize the cooling power of outdoor air to the greatest extent possible. During August 2007, shortly after the peak of the local cooling season, when the building was expected to be under mechanical control, this investigation of the airflow and thermal properties of the new building was undertaken to provide useful information about its early performance.