**1. Introduction**

Positive indoor environments can improve occupant comfort and well-being by inducing positive perceptual outcomes. Uncomfortable environments, including noise, improper temperature, humidity, dim lighting [1,2], poor air quality, and unpleasant smells [3,4], may impede the quality of life and negatively affect occupants' experiences [5,6]. Furthermore, prolonged exposure to suboptimal indoor environments may lead to adverse changes in individual health conditions. In order to ensure positive indoor environments for occupants, perceptual quality assessment has been introduced and extensively studied in recent years. Influenced by indoor environmental quality (IEQ), it is necessary and beneficial to explore how humans perceive and what effects the environment brings. While there is still a limited understanding of the intrinsic neurological and biological mechanisms of human perception, it is still worthwhile to investigate indoor environmental quality from this perspective.

Despite ongoing research efforts in this area, the underlying mechanisms linking environmental factors and their perceptual effects on users still need to be fully understood. Furthermore, as researchers explore these relationships, additional challenges emerge in terms of psychological and sociological methodologies. It is necessary for researchers and practitioners in built environments to address these issues. Therefore, this Special Issue aims to gather articles that discuss indoor environmental quality and occupant comfort. The articles in this Special Issue encompass different research categories, ranging from conceptual analyses and reviews to research papers. The studies presented here investigate the characterization and perception of both individual indoor environments as well as complex environmental interactions, along with their management and design implications. The focuses of these investigations include both theoretical aspects (including the relationships between environmental quality and psychological or physiological effects) and methodological aspects (including protocols and procedures for gathering objective and subjective data).
