The overall quality of the indoor environment in which people live, work and spend their time and artefacts remain, is the result from a complex integration of a large number of physical attributes. These attributes result from an integration of a large number of building components. Assessing the individual components and assessing attributes individually is important, but does not guarantee unambiguously a healthy, comfortable and safe indoor environment. Prescriptive solutions may support in arriving at the desired result, however, for innovation the performance based approach should be the point of departure and this starts with performance indicators to assess this performance. Within the ongoing EU FP7 Coordination Action PERFECTION a set of performance indicators has been developed to assess the overall quality of the indoor environment in buildings. The main focus is on issues such as comfort, health and safety, but also accessibility, positive stimulation of people and, more generally, sustainability have been covered. This paper describes the constraints that relate to the development of such a framework and the changes proposed resulting from the expert assessment. An example of an indicator description and evaluation procedure is provided. From a long list of indicators identified a first proposal for a list of so-called Key Indoor Performance Indicators (KIPI's) and their evaluation procedure has been derived. This list has been assessed by different experts in different settings through various data collection methods, such as interviews, workshops,and survey. The development work has been carried out through iterations. The long-term aim of the project is to help enabling the application of new building design and technologies that improve the impact of the indoor built environment on the human well-being. The presented KIPI-list is an important starting point for that.