This checklist of Santa Cruz Island, California, USA bees includes information from prior publications, a previous checklist by Robbin Thorp (Thorp, 2007), natural history collection specimens, and recent collections by the author. No observation records (i.e., iNaturalist) are used in this checklist. Not all specimens supporting this checklist were recently examined, and a few occurrences are considered dubious. Dubious records are annotated as such in the notes about the species. Recently examined specimens include all specimens from UC Santa Barbara and the American Museum of Natural History. In total, 129 taxa were recorded belonging to 5 families, 35 genera, and 126 species. Thorp also included several indications of morphospecies that are not included in this checklist, including Osmia sp. nr. exigua and 11 undetermined Nomada species. Morphospecies or estimated numbers of morphotypes are not included in this checklist. Taxonomy generally follows Ascher & Pickering, 2020. Subgenera are not listed in the checklist for species; however, their subgeneric placement is included if the subgenus is the lowest determination of a specimen (ex. Calliopsis (Micronomadopsis) sp.). Please note the collections, collectors, and determiners of the vouchers for each record. Many of the identifications of newly collected specimens were made by Jamie Pawelek. John S. Ascher supported prior surveys by Robbin Thorp. Every recorded specimen (example: J. S. Ascher, R. W. Thorp 2008-04-10 [AMNH]) indicates the collectors, and the digital collection record is found on the Bee Library Symbiota data portal (Seltmann et al 2021). Each voucher record is linked to further information about the specimen, including the specific location, specimen identifier, year collected, and depository. The checklist was created using the Bee Library, and an online version of the checklist can be found at https://library.big-bee.net/portal/checklists/checklist.php?clid=3. Acknowledgments: Many people helped create this checklist, including Dr. Douglas Yanega (UC Riverside) and Dr. Denise Knapp (Santa Barbara Botanic Gardens, Santa Barbara, California). Evan Hobson and Zoe Wood were authors of the previous version of the list (0.02). David Dewey supported pan trapping of specimens all over the island for several years. Lynn McLaren supported the collection of specimens and provided background research on prior checklists. Charlie Thrift processed and collected many of the newly collected specimens at UC Santa Barbara. This project is supported by the National Science Foundation via the "Extending Anthophila Research Through Image and Trait Digitization" project (DBI:2102006). References: Ascher, J. S., and J. Pickering. (2020). Discover Life bee species guide and world checklist (Hymenoptera: Apoidea: Anthophila). http://www.discoverlife.org/mp/20q?guide=Apoidea_species. Seltmann KC, Allen J, Brown BV, Carper A, Engel MS, Franz N, Gilbert E, Grinter C, Gonzalez VH, Horsley P, Lee S, Maier C, Miko I, Morris P, Oboyski P, Pierce NE, Poelen J, Scott VL, Smith M, Talamas EJ, Tsutsui ND, Tucker E (2021) Announcing Big-Bee: An initiative to promote understanding of bees through image and trait digitization. Biodiversity Information Science and Standards 5: e74037. https://doi.org/10.3897/biss.5.74037. https://library.big-bee.net Thorp, R. (2007). A List of Bees of Santa Cruz Island, CA. UC Santa Barbara: Cheadle Center for Biodiversity and Ecological Restoration. Retrieved from https://escholarship.org/uc/item/32s13481