GPR55 is an orphan Class A G-protein coupled receptor that recognizes a sub-set of cannabinoid CB1 and CB2 ligands, suggesting that GPR55 could belong to the endocannabinoid system. Lysophosphatidylinositol (LPI) has been proposed to be endogenous ligand for GPR55. However, GPR55 is still considered orphan receptor due to the lack of in vivo efficacy. The interest of GPR55 ligands as therapeutic agents is supported by the fact that this receptor is involved in diverse physiological and pathological processes such as inflammatory and neuropathic pain, metabolic disorder, bone and neuronal development, and cancer. Few potent GPR55 ligands have been identified to date due to an absence of information about salient features of GPR55, such as residues importance for binding and residues implicated in the GPR55 signaling cascade. High throughput screening of a large library of compounds from the Molecular Libraries Probe Production Centers Network (MLPCN) allowed the identification of different GPR55 chemical scaffolds, including ML192, a GPR55 antagonist. However, their potency and selectivity needs to be optimized in order to develop appropriate pharmacological tools or novel drugs to continue with the challenging goal of the validation of this receptor.