The 29 species and three subspecies comprising the imbecillus and rufus groups of the genus Philodromus in North America are described or redescribed, keyed, and illustrated. The imbecillus group contains six species, of which P. psaronius is described as new and the female of P. undarum Barnes is described for the first time. The rufus group contains 23 species and three subspecies, of which P. cubanus, P. distans, P. schicki, and P. bimuricatus are described as new-species, and P. rufus quartus as a new subspecies. P. inaequipes Banks, 1900 is proposed as a new synonym of P. minutus Banks, 1892, and P. michiganensis Levi, 1951 as a new synonym of P. peninsulanus Gertsch, 1934. P. mediocris Gertsch and P. minutus Banks are raised from synonymy, and P. pacificus Banks is raised from synonymy and made a subspecies of P. rufus Walckenaer.