Humans are a major source of indoor chemicals. Breath and sk Occupant-Related Chemical Transformations in emissions meaningfully contribute to the chemical composition of indoor air. Volatile organic compounds emitted by humans originate from endogenous sources (metabolic processes), and from exogenous sources (environmental exposure, diet, and personal care products). They can result from microbial activity and can lead to odor nuisance and decreased perceived air quality. The emitted compounds can undergo chemical transformations, such as ozone-initiated reactions, which produce a range of new compounds. The reactions of ozone with squalene and other constituents of skin oils have been shown to significantly alter the composition of indoor air and alter its OH reactivity. Dermal emissions may impact perceived air quality more than emissions via breath. The understanding of the effects of various environmental and personal factors (e.g., temperature, humidity, personal hygiene, diet, clothing, personal care products, age, sex, emotional state) on human emissions, their chemical transformations, and their consequences for indoor air quality, comfort, and health is limited. This chapter presents an overview of occupant emissions and the indoor air chemistry associated with them. Personal and environmental factors that may influence human emissions are discussed. Emerging research on the potential impacts of occupant emissions on perceived indoor air quality and human health is presented, and key research questions to advance our understanding of occupant-related indoor air chemistry are highlighted.