Lymantria monacha (L.) (Lepidoptera: Lymantriidae), the nun moth, is a Eurasian pest of conifers that has potential for accidental introduction into North America. To project the potential host range of this insect if introduced into North America, survival and development of L. monacha on 26 North American and eight introduced Eurasian tree species were examined. Seven conifer species (Abies concolor, Picea abies, P. glauca, P. pungens, Pinus sylvestris with male cones, P. menziesii variety glauca, and Tsuga canadensis) and six broadleaf species (Betula populifolia, Malus x domestica, Prunus serotina, Quercus lobata, Q. rubra, and Q. velutina) were suitable for L. monacha survival and development. Eleven of the host species tested were rated as intermediate in suitability, four conifer species (Larix occidentalis, P. nigra, P. ponderosa, P. strobus, and Pseudotsuga menziesii variety menziesii) and six broadleaf species (Carpinus caroliniana, Carya ovata, Fagus grandifolia, Populus grandidentata, Q. alba, and Tilia cordata) and the remaining 10 species tested were rated as poor (Acer rubrum, A. platanoidies, A. saccharum, F. americana, Juniperus virginiana, Larix kaempferi, Liriodendron tulipfera, Morus alba, P. taeda, and P. deltoides). The phenological state of the trees had a major impact on establishment, survival, and development of L. monacha on many of the tree species tested. Several of the deciduous tree species that are suitable for L. monacha also are suitable for L. dispar (L.) and L. mathura Moore. Establishment of L. monacha in North America would be catastrophic because of the large number of economically important tree species on which it can survive and develop, and the ability of mated females to fly and colonize new areas.