Several epidemiologic studies indicated a beneficial effect of tomato consumption in the prevention of some major chronic diseases. One of the main phytochemicals in tomato products is lycopene, an aliphatic hydrocarbon with 13 double bonds, 11 of them being conjugated. The molecule exists in trans-(all-E)-form as well as in several cis-(Z)-forms. Around 85% of the lycopene ingested comes from tomatoes and tomato products. Lycopene is absorbed together with lipids and lipid-soluble vitamins. Food processing as well as the type of food matrix affect the absorption of lycopene and other carotenoids. The main isomer in all food samples investigated was (all-E)-lycopene. In contrast, in plasma the main lycopene isomers were (all-E)-lycopene and (5Z)-lycopene. In several human intervention studies, the (all-E): (Z)-ratio of lycopene changed from 40:60 to 25-30:70-75 during the depletion period and returned approximately to the baseline values with intervention. Several hypotheses exist in literature to explain why lycopene is found in the human body as more than 50% (Z)-isomers in contrast to more than 85% (all-E)-lycopene in foods.