Interest for extracellular nucleotides has increased since the pioneer work of Burnstock in the early seventies. Research on cellular functions modulated by purines and pyrimidines has led to the identification and characterization of the different components of purine signaling, namely purinoceptors and ecto-nucleotidases. Receptors for tri- and diphosphonucleosides, known as P2 nucleotide receptors, are designated either P2Y receptors, for those coupled to Gproteins, or P2X for those which are ligand gated-ion channels. Ecto-nucleoside triphosphate diphosphohydrolase (NTPDase; EC 18.104.22.168), previously identified as ecto-ATPase, ecto-ATPDase or CD39, is now considered as the main ecto-nucleotidase responsible for the sequential hydrolysis of beta and gamma phosphates of tri- and diphosphonucleosides. More recently, research has been focused on the development of specific agonists and antagonists to P2 purinoceptors. The need to develop specific inhibitors for NTPDase to understand the role of this enzyme has clearly emerged. This paper covers the development of specific molecules targeting purinergic signaling, more specifically the inhibition of NTPDase and their impact on the different physiological systems.