The western black-legged tick, Ixodes pacificus Cooley & Kohls, is an important parasite and vector of disease agents that affect human and animal health in the western United States. This paper presents a review of all published California host records for I. pacificus. Unpublished data from public health, academic, and vector control agencies and researchers were reviewed as well. Host species were identified for each active life stage (larvae, nymph and adult). A total of 108 vertebrate species in three classes (Mammalia, Aves, and Reptilia) were identified as hosts for at least one life stage of I. pacificus. Adult I. pacificus were recorded from 29 species of mammals, 2 species of birds, and 1 reptile species. Nymphal I. pacificus were recorded from 30 species of mammals, 38 species of birds, and 8 reptile species. Larval I. pacificus were recorded from 29 species of mammals, 43 species of birds, and 8 species of reptiles. A table depicting the taxonomic classification of host species is provided. This review adds eight new host records to the California list of recognized vertebrate host species for I. pacificus.