This chapter explains factors that influence thermal comfort, and introduces assessment of thermal comfort. It explains how and why thermal comfort results in simulation outputs may be inaccurate, and how to achieve more accurate assessment of comfort through the post-processing of simulation results. The chapter shows how predicted mean vote (PMV) and predicted percentage of dissatisfied people (PPD) are used in dynamic simulations, and how thermal comfort can be improved by making changes in the design and using these parameters to assess alternative designs. The pioneering work by Fanger and subsequent related work provided input into several standards and other technical documents that are used by simulation tools as the basis for thermal comfort assessment. Therefore, the interpretation of thermal comfort results in simulation outputs requires special attention and further post-processing, in order to take into account expected human behaviour, rather than to rely on constant activity and one or two constant clothing levels throughout the year.