The chapter discusses the processes of human perception and experiencing, and of quality formation. In this context, definitions of relevant terms are re-visited and adapted to the presented, updated view, and different aspects of research into quality at large and into Quality of Experience are summarized. Using a conceptual model, the quality formation process is analyzed in view of different contexts and tasks, such as taking part in a quality test under controlled conditions, experiencing a video presentation or concert, or exploring a system or device when considering a purchase in a shop. We provide a short overview of different quality assessment methods, and outline related trends in QoE research.