Pterygium is an ocular surface disease of humans attributed to chronic ultraviolet-B (UV-B) exposure. Clinically, the condition involves invasive centripetal growth with associated inflammation and neovascularization. Prior clinical studies focused primarily on the clinical characteristics and surgical management of pterygia and, due to this fact, the pathogenesis of pterygia remains incompletely understood. However, considerable progress in this area has been achieved, providing additional insight into this complex disease. This recent evidence implicates anti-apoptotic mechanisms, immunological mechanisms, cytokines, growth factors, extracellular matrix modulators, genetic factors, viral infections, and other possible causative factors. Limited investigation regarding differences in pathogenesis of primary and recurrent pterygia has been performed. We summarize many of these recent discoveries concerning the pathogenesis of pterygia and describe reported differences between primary and recurrent pterygia.