The recent studies on the interaction of surfactants and fatty acids with lipids are inspired by the want of knowledge from several research fields of highest activity: identification of membrane rafts; membrane protein crystallization; formation of non-lamellar phases in membranes; membrane fusion. Detailed phase diagrams for lipid-surfactant and lipid-fatty acid mixtures, obtained in the last few years, reveal complicated mesomorphic and polymorphic behavior, including miscibility gaps and compound formation. Surfactant-induced non-lamellar to lamellar transitions in lipids and specific temperature-driven bilayer-micelle transitions represent extensions of the general three-stage model of membrane solubilization. Further research is required to construct phase diagrams as to delineate the principles of lipid-surfactant and lipid-fatty acid interactions for the variety of membrane lipid classes.