Multi-tenanted buildings are notoriously complex to manage due to heterogeneous populations, work objectives and styles, hours of operation and other factors, requiring an extraordinary amount of flexibility in building design and operation that often is not present. This research on energy efficiency and occupant behavior in multi-tenanted buildings investigates direct and indirect effects on energy use taking into account such factors as developer/owner requirements, building design and systems, construction outcomes, and building operator and occupant behavior. Field work was conducted between 2008 and 2012 in the Greater Philadelphia region and focused on comparison of two adjacent LEED certified buildings. Research design and methods were drawn from the tradition of comparative post occupancy evaluation (POE). Data collected and analyzed for this evaluation includes building owner, design team and tenant interviews, tenant and occupant focus groups, an occupant survey, building walk-through observations, utility bill and building automation system sensor log analyses, and building performance benchmarking. Three findings of this research stand out in highlighting the moderating nature of human behavior on building performance outcomes. They suggest that when building design and operation compromise usability, building occupants exhibit adaptive behaviors that can contradict the building’s design and performance intent. Disconnect between core and shell design and construction, and interior fit-out of tenanted spaces In the subject buildings the intent of the design– e.g., maximization of daylighting – is counteracted by interior organization of workspace. This disconnect is a prime example of an on-going challenge for building designers to acknowledge the extent to which energy efficient design strategies are affected by a dynamic occupant workforce and result in compromised outcomes in energy efficiency. Concurrently, they render the building less usable by both building occupants and the building operator.Diffused and confused locus of controlIn commercial building operation control over property management and function is diffused among the building developer/owner, manager, and tenants/occupants. A level of cooperation among these parties is therefore required to meet energy efficiency and related objectives. In this study, some level of confusion was discovered regarding control over lighting and HVAC. Occupant responses to these conditions are found to be diverse, may adversely affect building performance and result in lower satisfaction with the building environment.The role of direct feedback and lack of economic motivation A third finding of this study, which needs to be confirmed by additional research, is that occupants of commercial office space may lack economic motivation to conserve energy, especially if it comes at the cost of individual comfort in the workplace, even while claiming to hold pro-environmental values. This contradictory situation may be compounded by a lack of direct feedback regarding energy use, which seems to be especially common in multi-tenanted buildings in the U.S. The authors will discuss approaches to address challenges of energy management in multi-tenanted buildings. An important component of instilling these fixes is more accurate portrayal of the moderating affects of occupant behavior especially as relates to the usability of various green building systems and conflicts among organizational scales. This work was funded by the US Green Building Council, Liberty Property Trust and the US DOE Greater Philadelphia Innovation Cluster.