The discovery and development of green fluorescent protein (GFP) from the jellyfish, Aequorea victoria, has revolutionized studies on protein localization and dynamics by allowing direct observation of a protein's life history and pathway in living cells, previously only deduced from genetic, biochemical, or immunolabeling studies. Applied to the secretory membrane system, which regulates delivery of newly synthesized proteins and lipids to the cell surface, GFP-based studies are providing important new insights into the maintenance and biogenesis of organelles, as well as the origin, pathway, and fate of secretory transport intermediates.