Lipid bilayers are formed by spontaneous self‐assembly of amphiphilic lipid molecules. They represent the structure‐giving matrix and hydrophobic barrier of cell membranes and other biological membranes. Technically, they may form, for example, liposomes that are being used as smart drug delivery systems. The seminar aims at discussing the physical effects of amphiphilic or lipophilic peptides, drugs, and other membrane‐interacting solutes of natural or synthetic origin on the key properties of lipid membranes.