An account based on observations of the reproductive behavior of Serolis polaris is presented. Correlative additional information obtained from the examination of a large number of preserved specimens is discussed. Both the pre-copulatory behavior, and the copulatory position are described. Pre-adult females show sexual escape behavior. The pair of pereopods II are the only clasping appendages utilized in copulation. They are especially morphologically structured to perform this function. Marks, cuts and sores may be produced on the females by the rubbing movements of the clasping pereopods. Experiments show that when mature, males and females do not ingest food. A full discussion of all these behavioral aspects connected with reproduction is provided.