Field and herbarium research has revealed three newly recognized introduced and naturalized mosses in the northeastern United States. Rhytidiadelphus squarrosus, as that name is often applied in eastern North America, consists of a widespread common native species, R. subpinnatus, a carpet-forming moss of wet conifer and conifer-hardwood forest, and R. squarrosus in the strict sense, an introduced and naturalized moss that appears to be infrequent in eastern North America and restricted to weedy habitats such as lawns. Kindbergia praelonga is documented to occur on Nantucket Island, Massachusetts, in lawns in Nantucket town, indicating that it is a naturalized member of the bryoflora. There may also be native populations of this moss elsewhere in eastern North America, but this is unconfirmed. A moss of the southeastern and midwestern United States, Funaria flavicans, has been found with mature sporophytes in flower pots at a retail nursery on Nantucket Island in circumstances indicating it is an adventive. It may be a waif, or possibly a member of the naturalized bryoflora of Massachusetts, if in the future populations outside cultivation are found. New occurrences of a European moss, Psuedoscleropodium purum, from Maine, New Hampshire, Massachusetts, and in other places in eastern North America (Nova Scotia and North Carolina) add substantially to the previously known distribution of this moss. These new collections were in part from residential lawns and similar habitats outside of cemeteries where most of the previously known occurrences were concentrated, which may indicate that this moss is spreading.