© 2020 Elsevier Inc. To reduce the health burden of obesity, it is important to identify safe and practical treatments that are effective for weight loss while concurrently preventing weight regain. Diet-induced weight loss is usually followed by a concomitant increase in ghrelin secretion and feelings of hunger, which may compromise weight loss goals and increase the risk of weight regain. The aim of this review is to describe the status of knowledge regarding the impact of ketosis, induced by diet or exogenous ketones (ketone esters), on appetite and the potential mechanisms involved. Ketogenic diets (KDs) have been shown to prevent an increase in ghrelin secretion, otherwise seen with weight loss, as well as to reduce hunger and/or prevent hunger. However, the exact threshold of ketosis needed to induce appetite suppression, as well as the exact mechanisms that mediate such an effect, has yet to be elucidated. Use of exogenous ketones may provide an alternative to KDs, which have poor long-term adherence due to their restrictive nature. Ketone esters have been shown to have concentration-dependent effects on food intake and body weight in rodent models, with effects becoming apparent when 30% of total dietary energy comes from ketone esters (threshold effect). In humans, acute consumption of a ketone ester drink reduced feelings of hunger and increased satiety compared to a dextrose drink. With the emerging widespread acceptance of KDs and exogenous ketones in mainstream media and the diet culture, it is important to fully understand their role on appetite control and weight management and the potential mechanisms mediating this role.