The U.S. Fish and Wildlife Service (FWS), proposes to list the monarch butterfly (Danaus plexippus) as a threatened species and designate critical habitat under the Endangered Species Act of 1973 (the Act). They propose to list the monarch butterfly as a threatened species with protective regulations under section 4(d) (a “4(d) rule”). Finalizing this rule as proposed would add this species to the List of Endangered and Threatened Wildlife and extend the Act's protections to the species. We also propose to designate critical habitat for the monarch butterfly under the Act. In total, approximately 4,395 acres in Alameda, Marin, Monterey, San Luis Obispo, Santa Barbara, Santa Cruz, and Ventura Counties, California, fall within the boundaries of the proposed critical habitat designation.