Antimicrobial peptides are present in men, animals and plants and represent an important component of the innate immunity. Nevertheless they can also be generated through proteolytical digestion of food proteins. Thus, food proteins can be regarded not only for their nutritive value but also as a possible resource to increase the natural defence of the organism against invading pathogens. Consequently food proteins can be considered as component of nutritional immunity. Antimicrobial peptides generated from food proteins present the great advantage to be derived from harmless substances, therefore one can expect their safety for use in medicine and in food industry. Many biologically active peptides have been produced from food proteins, in particularly from milk proteins. The possibility that proteins can be tailored and their fragments modelled to achieve a particular function is recently giving rise to increased interest. This strategy has had particular success with food proteins like lactoferrin and lysozyme. Both bactericidal domains of these proteins have been extensively investigated. A number of short peptides with high bactericidal activity have been developed from the bactericidal domain of lysozyme through the strategy “tailoring and modelling”. Ovotransferrin, α-lactalbumin and β-lactoglobulin are further examples of food proteins which are a source of antimicrobial peptides. The observation that antimicrobial peptides can be generated through proteolytical digestion of parent proteins, which usually have another physiological function in the organism, led us to consider these latter as multifunctional molecules. This raises the question, whether multifunctionality is an intrinsic property of many proteins or limited to a few.