This thesis provides new knowledge on how to design comfortable passenger seats and provides recommendations for design and research. Although the first studies on passenger seat comfort appeared already 40 years ago, the activities and context have changed since then. In this thesis, relationships have been mapped out between activities (context level), anthropometric variables (human level), and seat characteristics (seat level) on the one hand, and comfort and discomfort perception of passengers on the other hand. Results obtained from experiments, performed on aircraft seats, train seats and car seats, provide a better and more practical foundation for these relationships.