Abstract: A modular staircase assembly having a plurality of individual interconnecting upper and lower stringer members including a means for coupling upper and lower stringer members and a means for interconnecting in longitudinal alignment adjacent stringer members. Affixed to each set of upper and lower stringer members is a tread support for supporting a tread which is pivotally couplable to the associated upper and lower stringer sections so that when assembled and one of the upper and lower stringer sections is slid relative to the other the tread support moves so as to maintain a substantially horizontal position. Rotatable foot pads and mounting pads coupled to either end of the assembled structure accommodate changes in orientation of the staircase assembly.