Many membranes in eukaryotic cells are inhomogeneous structures in which various membrane components are nonrandomly distributed, forming diverse types of 'domains.' Some membrane domains have long been well known, because they are sufficiently large, long-lived, and morphologically well defined to be characterized using classical microscopic and biochemical approaches. However, new technologies have revealed the presence in membranes of smaller, often highly dynamic 'nanodomains' that also play key roles in membrane function. Our current understanding of the diversity, the properties, and...