Lipid rafts are cholesterol-rich membrane domains which, having a different fluidity from lipids that surround them, regulate numerous membrane functions in eukaryotic cells. In recent years, rafts have been extensively studied because of the great interest the scientific community places on them. One of the reasons for such interest is their direct involvement in various diseases such as viral infection and, more specifically, in viral entry and the membrane fusion process whereby the virus in enveloped within the host’s cell membrane. This paper presents a study of what these lipid domains are, their structure, and in what sense they are involved in viral infection, taking HIV-1 as a model. The paper also includes an examination of the membrane models used to mimic and study these lipid domains, and a thermodynamic study of mixtures of different lipid composition (in order to obtain the proportions for the formation of lipid rafts in a single layer model, obtaining stable monolayers).