Phytochemical research has revealed that organic sulfur-containing compounds (OSCs) from Allium species exert biological effects, that might be beneficial in the treatment or prevention of a range of diseases, such as infections, cardiovascular and metabolic affections, cancers and related indispositions. Focusing physiological activities of these compounds in the context of cancer, it became clear from both epidemiological studies in men and experimental studies in diverse models, that the OSCs have a strong potential to prevent or to treat cancers even with selectivity against non-neoplastic cells. Though underlying mechanisms are not yet fully understood, several parts of their modes and mechanisms of action were elucidated: Pivotal molecular targets of as well chemoprevention as chemotherapy are metabolic, transporter or repair enzymes strongly affecting cell death, proliferation and formation of metastases. Accordingly effects are not restricted to the run of cell death programs, but they moreover comprise the strongly interdepending immune and inflammatory systems. Respectively, several hypotheses exist which are based on chemical properties of sulfur as the “pharmacophor” of the compounds appearing in up to ten different oxidation states (−2 to +6). Hence compounds can undergo redox-reactions and electrostatic interactions, making reactive oxygen species (ROS) a key feature of their mechanisms of action.