Numerous peptides interact more or less specifically with lipid membranes. Membrane active peptides are an integral part of the first line of host defence against infections in a wide variety of organisms and can show broad-spectrum antimicrobial activity. The interaction between antimicrobial peptides (APMs) and bacterial lipid membranes leads to loss in membrane integrity, either by formation of transmembrane pores or by a surface-associated carpet mechanism, and there are hence no obvious mechanisms for development of resistance. We study both natural AMPs and designed AMP-mimetic peptides for various therapeutic applications.