Lipids are probably best known as the building blocks of cellular membranes. The membranes of eukaryotic cells separate functional compartments, and the plasma membrane provides a barrier between the cell and its environment. Cell membranes consist of lipid bilayers — a concept that was first suggested in the 1920s, but was not firmly established until the early 1970s. On page 414 of this issue, Michael Edidin looks back at how the lipid-bilayer model has developed over the past 100 years, and forward to a new integrated model that incorporates the dynamic interplay between components of cell membranes.

The cell nucleus also contains lipids, some of which have a structural role in the nuclear-envelope fraction. However, after removing nuclear membranes by treatment with detergent, the remaining lipid fraction is considerable. On page 349, Robin Irvine discusses these intranuclear lipids — mostly inositol lipids — and their role in signalling systems in the nucleus.

Sphingosine was named after the Greek mythological creature the sphinx — because of its enigmatic nature — and sphingosine-1-phosphate is now revealing itself as a multifunctional signalling molecule. Sarah Spiegel and Sheldon Milstien (page 397) review data that implicate sphingosine-1-phosphate as a vital lipid mediator that regulates cell growth and suppresses programmed cell death, and as a ligand for cell-surface receptors.

Also in this issue, on page 409, Juan Bonifacino and Jennifer Lippincott-Schwartz discuss coat proteins. Recent findings indicate that the job of coat proteins goes beyond their widely accepted roles as the mediators of selective transport between membrane-enclosed compartments. New functions in long-range transport have been proposed, and coat proteins might participate in the differentiation of organellar domains.