Antimicrobial peptides play a key role in many biological and physiological functions of living organisms and are an attractive starting point for the development of novel drugs. The group is strongly involved in the study of beta-defensins that have been demonstrated to have potent antimicrobial activity against gram-positive and gram-negative bacteria, fungi, viruses and parasites. Thus, defensins represent an excellent starting point for the development of new molecules able to fight infectious diseases. In this scenario, we have designed a number of analogues that have increased potency and reduced sensitivity to high ionic strength. Notwithstanding these promising features, defensins show some drawbacks such as extremely complicated and expensive synthetic protocols. In an attempt to overcome this limiting factor, the group has designed a cyclic mini defensin carrying the crucial active regions of the native sequences, which is not toxic, exerts effective antibacterial activity and is stable in blood. Given these features, this molecule may be considered a novel weapon in the fight against infectious diseases. The group is also working on other targets such as peptides derived from the antimicrobial fish peptide mixinidina. This topic is a very active and a open research field which is emerging as a key approach for solving the problem of antimicrobial resistance.