Caffeine is one of the most frequently consumed substances worldwide. It is present in some common beverages such as tea and coffee and in a variety of drugs, particularly analgesics. Its main mechanisms of action include inhibition of phosphodiesterase enzyme and adenosine receptors; its effects involve the whole body. In recent years there has been a debate in the scientific literature over the relationship between caffeine and the kidney and its possible toxicity. Several experimental studies have demonstrated that caffeine may exacerbate some pathological conditions such as polycystic disease and proteinuria, while others have underlined its protective effects in specific situations. While awaiting new, in-depth studies that will help to solve the debate, we can conclude that there is currently no evidence contraindicating the consumption of moderate quantities of caffeine by healthy subjects or kidney patients.