Abstract Some of the most relevant aspects of the feeding behaviour of the rat (Rattus norvegicus, Berkenhout, 1769) were examined with particular interest in the data collected on wild rats and in natural environments. The rat is considered as an omnivore and generalist species, but both in the wild and in the laboratory marked individual differences were recorded in food preferences and diet spectrum, which probably allow the natural populations to exploit a great number of habitat resources. A number of causes were identified as responsible of these differences: early pup differentiation; mother's and conspecifics' influences, etc. The importance of animal food in the rat diet is also variable. The diet of non-commensal rat colonies was examined with special reference to the predatory behaviour, which is a common habit in natural populations; furthermore the insorgence of "local traditions" such as the Mollusc predation was considered. The hypothesis of social transmission of this feeding habit, widespread in the Po river Basin and Delta, was discussed and confirmed. The hoarding behaviour, well studied under laboratory conditions, was rarely recorded in the wild. It is supposed to be a useful mechanism that the rat uses to cope with particular conditions (e.g. surplus of food, lactating females) but this species cannot be defined as a "natural hoarder". The degree of neophobia is variable in populations that interact with man and it is practically absent in non-commensal populations. This confirms that it is a defensive strategy resulting from the commensal habit of the rat and not a fixed behavioural characteristic of this rodent species. The stealing of food between animals, kleptoparasitism, was frequently observed in confined rat groups in laboratory but rarely described in the wild. It is compared with the "worker-parasite" relationship supposed to be a kind of division of labour. The most important components of the foraging behaviour of the rat, are: the constant sampling of al1 the potential foods that brings the populations to a noteworthy adaptability to the change of available resources; the social interactions among individuals (mother-pups, adult-adult) that are very important in influencing the food preferences and, eventually, the food avoidance; the use of feeding-places, which is considered as a fundamental trait of the foraging behaviour of the rat, working as an information-centre of the animals. Riassunto Sono stati esaminati alcuni dei più importanti aspetti della strategia alimentare del ratto, Rattus norvegicus (Berkenhout, 1769) considerando in particolare il comportamento dei selvatici e i lavori in natura. Le marcate differenze individuali nelle preferenze alimentari ed il campionamento continuo di tutte le potenziali fonti alimentari, permettono alle popolazioni naturali di sfruttare un gran numero di risorse dell'ambiente, adattandosi alle sue variazioni. I1 comportamento di accumulo, ben evidenziato in laboratorio ma scarsamente documentato in natura, sembra nel ratto un meccanismo utilizzato solo per far fronte a situazioni particolari (es. surplus di cibo, allattamento). I1 grado di neofobia è variamente modulato in popolazioni che hanno un rapporto con l'ambiente umano e assente nelle popolazioni non commensali. Molto importanti risultano le interazioni sociali fra gli individui (madre-piccoli, adulti-adulti) nell'influenzare le scelte alimentari. Vengono discussi i dati relativi alla predazione su Molluschi che confermano l'ipotesi di una trasmissione delle informazioni riguardo alla scoperta di nuovi alimenti e delle tecniche di apertura del guscio. La formazione di mense viene interpretata come un fondamentale aspetto del comportamento di foraggiamento del ratto, rilevante come centro per lo scambio di informazioni fra gli animali.