Betulin, a pentacyclic triterpene and a plant pentacyclic triterpene metabolite, can be found in large quantities in the outer bark of the birches (Betula, Betulaceae). Betulinic acid, obtained by betulin oxidation, is also abundantly present in nature. Both compounds show a wide spectrum of biological and pharmacological properties, such as anti-HIV, anti-inflammatory, and, considered the most important, anti-cancer. Although the specific mechanism of action of betulin against malignant cells is still a subject of detailed research, the activity of betulin acid has been linked to the induction of the intrinsic pathway of apoptosis. As this process occurs with the sparing of non-cancer cells, and the induction of apoptosis can occur under conditions in which standard therapies fail, both substances seem as promising experimental anti-cancer drugs. The aim of this review is to comprehensively summarise the potential of betulin and betulinic acid, both in vitro and in vivo. The discovery, structure, organic synthesis and derivatives forming were shortly described. Also, the potential molecular mechanisms of action and numerous medical applications of betulin and betulinic acid were presented, including previous studies of anti-cancer activity of the compounds, with listed cancer cell types susceptible to therapy.