The endoplasmic reticulum forms the first compart-ment in a series of organel es which comprise the secretory pathway. It takes the form of an extremely dynamic and pleomorphic membrane-bounded network of tubules andcisternae which have numerous different cel ular functions. In this review, we discuss the nature of endoplasmic reticulum structure and dynamics, its relationship with closely associated organel es, and its possible function as a highway for the distribution and delivery of a diverse range of structures from metabolic complexes to viral particles.