BACKGROUND: Parkinson's disease (PD) is the second most common neurodegenerative disorder with cognitive impairment as a prime non-motor symptom. Biomarkers can assist in detecting cognitive impairment, which normally follows movement dysfunction, and also assist in the differentiation of PD patients with and without cognitive dysfunction, facilitating the early diagnosis and disease management while also allowing for timely therapeutic intervention. SUMMARY: Here, we have reviewed the biomarkers of Parkinson's disease from different sources i.e., body fluids (CSF, blood, salivary, urine and tear) and tissues (gut and skin), along with the techniques used for the detection of these biomarkers. We further discuss the importance of biomarker validation and the significance of cohort studies in biomarker discoveries. KEY MESSAGE: The chapter is aimed at updating the knowhow of the disease biomarkers that may assist differentiation of these overlapping entities.