This book presents extensive research on the quality of 360 video perceived by users with HMDs. The book aims to develop a set of standard guidelines for the systematic visual quality assessment of 360 videos. Firstly, conventional subjective test methods such as Absolute Category Rating (ACR) and Double Stimulus Impairment Scale (DSIS) are applied to evaluate video quality, alongside the Modified ACR (M-ACR) method newly proposed. Building on the reliability and general applicability of the procedure across different tests, a methodological framework for 360 video quality assessment is then presented. The author also analyzes simulator sickness to investigate the impact of different influencing factors. The insights gained on simulator sickness related to 360 video contribute to a better understanding of this particular use case of VR and can help to improve comfort among users by suggesting improvements in the technical specifications of 360 video and HMD technology and thus improving QoE.