In this review article we discuss the forces acting between hydrophobic surfaces and between air-water interfaces coated with lipids. The main focus is on the short-range interactions between monoglyceride coated surfaces. The forces generated by this class of compounds are compared with those obtained in the presence of phospholipids and surfactants with sugar headgroups. The experimental results show that the forces generated when the lipid chains are in a fluid state generally are stronger compared to when the hydrocarbon chains are in a frozen state. This is the case despite that the area per molecule is larger in the former case. This result can most easily be rationalized provided the molecular origin of the short range repulsion is of steric rather than a hydration force, as recently suggested by Israelachvili and Wennerström (J. Phys. Chem. 96, 520-531 (1992)). In this review article we also present three techniques that can be utilized for studying interactions between lipid layers. The osmotic stress technique that provides information about forces in liquid crystalline phases, the interferometric surface force technique that is employed for studying forces between solid surfaces, and the thin film balance utilized in order to study the interactions between two air-liquid interfaces.