This narrative review explores the role of microbiota, tryptophan (Trp), and aryl hydrocarbon receptors (AhR) in Parkinson's disease (PD). The review highlights the interplay between the gut microbiota, the Trp-kynurenine (KYN) pathway, and AhR signaling in PD pathogenesis. The gut-brain axis is central to this process, with dysbiosis in the gut microbiota linked to neuroinflammation and the spread of α-synuclein, a key pathological feature of PD. The review suggests that peripheral kynurenine levels and AhR ligands are closely related to gut Trp metabolism and should be studied alongside microbiota composition. This approach could help identify subpopulations of PD patients with disturbed microbiota-Trp-KYN-brain triads, who might benefit from Trp metabolism modifications. The Trp-KYN pathway is a major route of Trp metabolism, producing various bioactive compounds, including kynurenines, which have both neuroprotective and neurotoxic effects. The AhR, a transcription factor, is activated by various ligands, including kynurenines, and plays a role in immune regulation and neuroprotection. The review discusses the impact of AhR signaling on PD, noting that AhR agonists may have anti-inflammatory effects and could be beneficial in PD treatment. Dietary interventions, including Trp-rich foods and probiotics, are suggested as potential therapeutic approaches. The review emphasizes the importance of a balanced diet in maintaining gut microbiota diversity and Trp metabolism. It also highlights the role of physical exercise in improving Trp availability and gut microbiota composition. Overall, the review underscores the complex interactions between the gut microbiota, Trp metabolism, and AhR signaling in PD, suggesting that targeting these pathways could offer new therapeutic strategies for the disease.This narrative review explores the role of microbiota, tryptophan (Trp), and aryl hydrocarbon receptors (AhR) in Parkinson's disease (PD). The review highlights the interplay between the gut microbiota, the Trp-kynurenine (KYN) pathway, and AhR signaling in PD pathogenesis. The gut-brain axis is central to this process, with dysbiosis in the gut microbiota linked to neuroinflammation and the spread of α-synuclein, a key pathological feature of PD. The review suggests that peripheral kynurenine levels and AhR ligands are closely related to gut Trp metabolism and should be studied alongside microbiota composition. This approach could help identify subpopulations of PD patients with disturbed microbiota-Trp-KYN-brain triads, who might benefit from Trp metabolism modifications. The Trp-KYN pathway is a major route of Trp metabolism, producing various bioactive compounds, including kynurenines, which have both neuroprotective and neurotoxic effects. The AhR, a transcription factor, is activated by various ligands, including kynurenines, and plays a role in immune regulation and neuroprotection. The review discusses the impact of AhR signaling on PD, noting that AhR agonists may have anti-inflammatory effects and could be beneficial in PD treatment. Dietary interventions, including Trp-rich foods and probiotics, are suggested as potential therapeutic approaches. The review emphasizes the importance of a balanced diet in maintaining gut microbiota diversity and Trp metabolism. It also highlights the role of physical exercise in improving Trp availability and gut microbiota composition. Overall, the review underscores the complex interactions between the gut microbiota, Trp metabolism, and AhR signaling in PD, suggesting that targeting these pathways could offer new therapeutic strategies for the disease.