The adenosine A2A receptor (A2AR) is highly concentrated in the striatum, and a therapeutic target for Parkinson’s disorder (PD) and Huntington’s disease. High affinity and selective radiolabeled A2AR antagonists can be important research and diagnostic tools for PD. Positron Emission Tomography (PET) can play an important role by measuring radiolabeled A2A antagonists non-invasively in the brain. However, till date no complete review on A2AR PET ligands is available. The present article has been therefore focused on available PET tracers for A2AR and their detailed biological evaluation in rodents, nonhuman primates and humans. Drug design and development by molecular modeling including new lead structures that are potential candidates for radiolabeling and mapping of cerebral A2ARs is discussed in the present article. A brief overview of functions of adenosine in health and disease, including the relevance of A2AR for PD has also been presented.