The peptide lactoferricin (Lfcin) can be released from the multifunctional protein lactoferrin (LF) through proteolysis by pepsin under acidic conditions, a reaction that occurs naturally in the stomach. Lfcin encompasses a large portion of the functional domain of the intact protein, and in many cases it not only retains the activities of LF but is more active. Lfcin possesses strong antimicrobial and weak antiviral activities, and it also has potent antitumor and immunological properties. This review covers the current state of research in this field, focusing on the many beneficial activities of this peptide. Throughout we will discuss the breadth of Lfcin activity as well as the mechanism of action. Many recent studies have drawn attention to the fact that the main site of action for the peptide may be intracellular. In addition the results of structural and dynamic studies of Lfcin are presented, and the relationship between structure and activity is explored.