Since the early 1960s, a series of potentially mutagenic and carcinogenic xenobiotics have been identified in foods, resulting from chemical changes induced by processing. The toxic effects have been extensively studied and demonstrated in experimental animals and human cells and tissues; human clinical and epidemiological studies, however, are lacking. Chapter 10 features eight types of such potentially harmful substances (i.e., acrylamide, benzene, biogenic amines, ethyl carbamate, furan and methylfurans, heterocyclic aromatic amines, 3-MCPD and 3-MCPD esters, and nitrosamines). For each one, their chemical structures, occurrence in foods, mechanisms of formation, influencing factors, mitigating strategies, and toxicological aspects are discussed. With the exception of certain biogenic amines, which have some health benefits, and furan, which contributes to the typical aroma of certain foodstuffs (e, g., roasted coffee), substances herein addressed are known for their possible detrimental effects on health. Efforts have been made to minimize their formation, principally by improving the processing and home preparation methods. However, care should be taken that mitigation strategies do not undermine microbial safety and desirable sensory properties.