This study compares the electricity consumption of two buildings, of similar architectural design, in Simba Office Park, Sandton, in Johannesburg. One of the buildings (Block AB) has not been retrofitted for energy efficiency, whilst the other building (Block C) is a retrofitted building. The hypothesis postulates that the retrofitted building would use less energy than the non-retrofitted one. In this investigation, electricity consumption data based on meter readings was collected for the same blocks over the period March 2009 to April 2010. The retrofitting measures were documented and the associated costs noted; and interviews were conducted with key personnel. It was found that energy consumption for Block C far exceeded that for Block AB. Thus, in this case, retrofitting did not reduce electricity consumption. The results demonstrate that in order to fully understand energy use, data collection and analysis must be ongoing. This book therefore, provides some considerations regarding retrofitting commercial buildings. This information will be useful to commercial building owners, developers, engineers, building developers, and building managers.