One of two multimeric complexes that forms a membrane vesicle coat. COPII is best characterized in S. cerevisiae, where the subunits are called Sar1p, Sec13p, Sec31p, Sec23p, and Sec24p. Vesicles with COPII coats are found associated with endoplasmic reticulum (ER) membranes at steady state. [ http://www.ncbi.nlm.nih.gov/pubmed/11252894 GOC:dph GOC:mah GOC:ascb_2009 GOC:tb ]