Biomembranes surround every living cell and separate it from the outer environment. They comprise a lipid bilayer, which forms an efficient hydrophobic barrier and in which membrane proteins are embedded. In addition to large membrane proteins, a class of much smaller membraneactive peptides has raised considerable interest in the area of biophysics. Many membrane-active peptides are involved in events that permeabilize or remodel the cellular membrane, which makes them particularly attractive for biotechnological and pharmaceutical applications. These peptides exhibit a broad range of diverse membrane-related activities, and can act as cell-penetrating carriers, antibiotic drugs, or powerful fusogenic agents. To further our understanding of these fascinating peptides, two meetings were held in Europe in 2010, and papers from these meetings are the basis of this special issue. Biophysics of membrane-active peptides was the theme of the 455th seminar organized under the auspices of and funded by the Wilhelm und Else Heraeus-Foundation, held in Bad Honnef, Germany, April 2010. Current research and recent findings on membrane-active peptides were highlighted in focused sessions on peptide structure and dynamics, antimicrobial peptides, cell-penetrating peptides, fusogenic peptides, and proteins, new and notable, besides several outstanding after-dinner talks. As a continuation of two previous international meetings on membrane-active peptides, in Lisbon in 2007 and Berlin in 2005, this topic has now established a tradition amongst European biophysicists. More than 30% of the participants in Bad Honnef were preand postgraduate students, many of whom gave oral presentations of their posters. The Joint Australia–Croatia Workshop on Antimicrobial Peptides, AMP 2010, was held in Split, Croatia, in August 2010, and included a summer school for PhD students in biophysics. The sessions covered computer modeling studies, nuclear magnetic resonance methods and drug design, mechanisms of action, and natural and synthetic analogues. The workshop brought together experimentalists and theoreticians interested in understanding the functional modes of antimicrobial peptides and their development as antibiotics. This European Biophysical Societies’ Association-sponsored conference was open to an international audience and highlighted intra-European as well as intercontinental contacts in explicit collaboration sessions. The present EBJ special issue comprises a collection of up-to-date research papers devoted to membrane-active peptides, yielding topical insights on peptide–lipid interactions, three-dimensional structure analysis, mechanisms 455th WE-Heraeus-Seminar ‘‘Biophysics of Membrane-Active Peptides’’ (Bad Honnef, 11–14 April 2010). AMP 2010, Australia– Croatia Workshop on Antimicrobial Peptides (Split, 9–13 August 2010).