This chapter presents an introduction to the complex geometry of cubic phases, followed by an experimental survey of the compatibilities of lipidic mesophases and their relevance to this novel crystallization approach. It introduces the structural aspects of lipidic cubic phases and their compatibility with respect to a variety of additives. Membrane proteins have failed to yield crystals of adequate sizes and sufficient order that allow their three-dimensional structures to be determined to high resolution by crystallographic analysis. The fluid mosaic model of biological membranes has proven a valid concept and has had an enormous impact on our understanding of membranes. Lipidic mesophases are materials consisting of water and lipid that form the fourth state of matter, liquid crystals. The chapter discusses the compatibilities of such lipidic systems upon incorporation of a variety of additives into the two separate and complementary loci—the hydrophilic channels and the amphiphilic curved bilayers.