Oleuropein is an antioxidative polyphenolic compound in the olive oil responsible for its bitter taste and oxidative stability. It is the major compound in the olive leaves and fruits, while in an olive oil is much less abudant. Its impacts on human health mostly depend on its quantity in the olive oil (which is very variable), and to a lesser degree on the absorption and metabolism in the human organism. Oleuropein has shown antioxidative, anti-inflammatory, cardioprotective, antidiabetic, antiproliferative, neuroprotective, anti-infective, gastroprotective, hepatoprotective and osteoprotective effects. Although some of its effects are exerted through specific mechanisms of action, most of them are exerted through its antioxidative activities and its ability to inhibit intracellular signaling pathways and expression of certain proteins at the transcriptional level. Antioxidative effects of oleuropein are exerted through its direct (such as scavenging of free radicals and radical chain breaking, reducing activity and chelation of metal ions) and indirect (regeneration of an endogenous antioxidative system and modulation of a gene expression of some antioxidative enzymes) mechanisms of action. Anti-inflammatory effects are exerted through the inhibition of some signaling pathways resulting in an reduced expression of proinflammatory mediators, cytokines and enzymes. Cardioprotective effects include antihypertensive, hypolipemic, anti-atherogenic and anti-ischemic effects. They are based on the inactivation of the oxidative molecules, inhibition of the lipid peroxidation, inhibition of NO and adhesion molecules expression, platelet aggregation inhibition, on the modulation of lipid profile and their metabolism, and on antiarrhytmic mechanisms. Antidiabetic effects are based on the modification of the glycemic parameters, protective impacts on β-cells in the pancreas, and increased cellular insulin sensitizing. Anticancer effects are based on the antiproliferative, antimetastatic and antiangiogenic activities of oleuropein, while neuroprotective effects are based on the antiamyloidogenic and antioxidative activities. Anti-infective effects include antibacterial (e.g. MRSA, Salmonella, Pseudomonas aeruginosa), antiviral (HIV-1, RSV, Para 3), antimycoplasmatic and antiparasitic (Toxoplasma gondii) activities. Gastroprotective effects are based on the antioxidative activities, as well as the hepatoprotective effects, which are also based on the antisteatogenic activities. Osteoprotective effects of oleuropein are based on the modification of the inflammatory parameters in postmenopausal osteoporosis and the stimulation of the osteoblastogenesis, while its impacts on the skin include antioxidative, anti-inflammatory and regenerative activities.