Twenty-six species of nemerteans are recorded as occurring in Danish waters. All were identified on the basis of internal characters. but the external appearance of each species is thoroughly described to allow other than the systematist to identify living specimens. For the same reason four colour plates. comprising nearly all the described species. are included. A few of the Danish nemerteans are shown to be euryhaline, but the majority are stenohaline. Of the latter nearly all are truly marine. while a few are adapted to brackish water. The abundance of species on muddy bottoms. from which a large part of the material was collected. seems to be closely related to the abundance of suitable food organisms.