This chapter focuses on mycotoxins, which are natural, secondary metabolic products of molds, in contrast to the primary metabolism products that often form under specific temperature and humidity conditions. The most important mycotoxin-producing fungi belong to the genera Aspergillus, Penicillium, and Fusarium. To date, several hundred mycotoxins have been identified, and human exposure primarily occurs through contaminated foods and in specific workplaces, such as agriculture, recycling facilities, or grain mills. The health effects of mycotoxins vary widely, ranging from cytotoxic, hepatotoxic, and nephrotoxic to immunosuppressive, estrogenic, and even genotoxic and carcinogenic. Therefore, a brief description of the chemical-physical characteristics and human exposure to various mycotoxins, their primary health risks, toxicokinetic properties, and references to further scientific literature is provided. The primary objective is to present detailed information on their occurrence in human matrices such as blood, urine, and breast milk. For this background, detailed information is provided on mycotoxins like aflatoxins, ochratoxin A, deoxynivalenol, nivalenol, fusarenon-X, T-2 toxin, fumonisins, zearalenones, citrinin, patulin, sterigmatocystin, enniatins, and alternariol.