The hemlock woolly adelgid (HWA), Adelges tsugae, is causing widespread mortality of eastern hemlock, Tsuga canadensis, in the eastern U.S. In the West, HWA causes negligible damage to western hemlock, Tsuga heterophylla. Host tree resistance and presence of endemic predators may be contributing to the relative tolerance of western hemlock. Field surveys of the predator community associated with HWA infestations on 116 T. heterophylla at 16 locations in Oregon and Washington were conducted monthly from March 2005 through November 2006. Predators collected represent at least 54 species in 14 families including, in order of abundance, Derodontidae, Chamaemyiidae, Coccinellidae, Hemerobiidae, Cantharidae, Miridae, Reduviidae, Syrphidae, Chrysopidae, Coniopterygidae, Staphylinidae, Anthocoridae, Nabidae, and Raphidiidae. Laricobius nigrinus (Derodontidae) and Leucopis spp. (Chamaemyiidae) are the dominant predators. The remaining predators represent a diverse community potentially attacking HWA. The phenology of immature and adult predators suggests temporal partitioning of prey across all seasons. Conwentzia californica (Coniopterygidae), Semidalis angusta (Coniopterygidae), Hemerobius pacificus (Hemerobiidae), Chrysoperla downesi (Chrysopidae), Mulsantina picta (Coccinellidae), Exochomus quadripustulatus (Coccinellidae), Harmonia axyridis (Coccinellidae), Leucopis argenticollis (Chamaemyiidae), Leucopis atrifacies (Chamaemyiidae), and Syrphus opinator (Syrphidae) have been successfully reared from larvae to adult on a diet of HWA in the laboratory. Field collected larvae of L. nigrinus and adults of Dichelotarsus piniphilus (Cantharidae) have been observed feeding on HWA eggs in the laboratory.