Vertical docking connector

An electrical connector comprises a main housing (102) having a mating face (104) and a mounting face (106), and a plurality of contact modules (136) received in said main housing. Each of said contact modules includes an upper contact module (200) and a lower contact module (202) joined to said upper contact module along side edges of said upper and lower contact modules. Each of said upper and lower contact modules includes a contact housing (240, 260) holding contacts including pairs of signal contacts (120) and individual ground contacts (122). Each said lower contact module includes an upper surface (268) and a slot (280) and a rail (284) proximate said upper surface, and each said upper contact module includes a lower surface (302) and a slot (320) and a rail (310) proximate said lower surface. Each said slot on said upper and lower contact modules is configured to receive said rail on the other of said upper and lower contact modules such that said upper and lower contact modules are slidably joined to