Kynurenine is an amino acid derivative found in the body after the breakdown of the essential amino acid, tryptophan, and is involved in a number of physiological and neurological pathways. As an endogenous indole, kynurenine is a crucial metabolite of tryptophan and has been linked to improved immune system functioning and neuroprotection. As such, it has been studied as a possible therapeutic target in neurodegenerative diseases, such as multiple sclerosis, depression, and Alzheimer’s disease. Additionally, kynurenine has been used in animal research as a marker of inflammation and to study the effects of diet and nutrition on health outcomes. This research has expanded to humans, and kynurenine has been recently studied in humans for its role in modulating immune responses and its potential therapeutic applications.