"Phalanx is a self-perpetuating, non-secret, Senior organization, formed at the Institute in 1912 for the purpose of fostering and keeping alive Rensselaer spirit and tradition among the student body." Each spring, during a baseball game or track meet, members of the Phalanx "tapped" men to become new members. As "Taps" played, the current members of the society would line up on the '86 Field in the ancient Phalanx formation. At this point, a member would outline the history and purposes of the society. The Phalanx men then approached the audience of students to tap the new members. When the tapping was completed, members and initiates formed the Phalanx and marched from the field. [The Polytechnic, May 23, 1929] Men were chosen for membership based on participation in student activities and "unselfish interest in the advancement of the school." A maximum of fifteen men could be chosen each year. Any graduate or person connected with the Institute "who has increased the welfare of the Institute by her or his personal activity" could also be elected to the society. A White Key society for sophomores was formed in 1937.

In 1971, membership was opened to student leaders from all classes including graduate students and the maximum membership restriction was abolished. Tapping took place during home hockey games from 1974 to 1982 in an attempt to publicize the society. By 1983, the tapping, initiation ceremony and dinner were combined into one event. From then on juniors, seniors and graduate students could be nominated to the society.