Carney, DanielRaj, NirmalBai, YangBerger, JoshuaBlanco, CarlosBramante, JosephCappiello, ChristopherDutra, MaíraEbadi, RezaEngel, KristiKolb, EdwardHarding, J. PatrickKumar, JasonKrnjaic, GordanLang, Rafael F.Leane, Rebecca K.Lehmann, Benjamin V.Li, ShengchaoLong, Andrew J.Mohlabeng, GopolangOlcina, IblesPueschel, ElisaRodd, Nicholas L.Rott, CarstenSengupta, DipanShakya, BibhushanWalsworth, Ronald L.Westerdale, Shawn2024-05-032024-05-032023Carney, D., Raj, N., Bai, Y., Berger, J., Blanco, C., Bramante, J., Cappiello, C., Dutra, M., Ebadi, R., Engel, K., Kolb, E., Harding, J. P., Kumar, J., Krnjaic, G., Lang, R. F., Leane, R. K., Lehmann, B. V., Li, S., Long, A. J., … Westerdale, S. (2023). Snowmass2021 cosmic frontier white paper: Ultraheavy particle dark matter. SciPost Physics Core, 6(4), 075. https://doi.org/10.21468/SciPostPhysCore.6.4.075https://hdl.handle.net/1911/115540We outline the unique opportunities and challenges in the search for "ultraheavy" dark matter candidates with masses between roughly 10 TeV and the Planck scale mpl≈1016 TeV. This mass range presents a wide and relatively unexplored dark matter parameter space, with a rich space of possible models and cosmic histories. We emphasize that both current detectors and new, targeted search techniques, via both direct and indirect detection, are poised to contribute to searches for ultraheavy particle dark matter in the coming decade. We highlight the need for new developments in this space, including new analyses of current and imminent direct and indirect experiments targeting ultraheavy dark matter and development of new, ultra-sensitive detector technologies like next-generation liquid noble detectors, neutrino experiments, and specialized quantum sensing techniques.engExcept where otherwise noted, this work is licensed under a Creative Commons Attribution (CC BY) license. Permission to reuse, publish, or reproduce the work beyond the terms of the license or beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Journal articleSciPostPhysCore_6_4_075https://doi.org/10.21468/SciPostPhysCore.6.4.075