COPI is a coat protein complexe. COPI vesicles that surround the Golgi stack were first implicated in the anterograde movement of cargo, and then in the retrograde movement of Golgi enzymes.

See also:

 COPII

References

 Storrie B, Pepperkok R, Nilsson T. Breaking the COPI monopoly on Golgi recycling. Trends Cell Biol. 2000 Sep;10(9):385-91. PMID: #10932096#

 Rabouille C, Klumperman J. Opinion: The maturing role of COPI vesicles in intra-Golgi transport. Nat Rev Mol Cell Biol. 2005 Oct;6(10):812-7. PMID: #16167055#