<p>Multi-material topology optimization (MMTO) has emerged as an effective method to leverage different candidate materials throughout topology-optimized designs. Multi-material multi-joint topology optimization (MM-MJ-TO) is an extension of MMTO that improves the manufacturability of design solutions by considering the joining between dissimilar materials. A limitation of MM-MJ-TO is that it can only consider adhesive or welded joints. The objective of this work is to develop a methodology for MM-MJ-TO that considers mechanical fasteners such as bolts, screws, or rivets. For this, three new constraints are introduced to the MM-MJ-TO problem statement: A fastener width constraint is developed to restrict joint elements to localized patches that indicate optimum fastener locations. A fastener access constraint ensures the fasteners can be inserted at these locations by limiting the surrounding structural material thickness. For two-sided fastener configurations (e.g., bolt &amp; nut assembly), accessibility is enforced on both sides of the interface, while for one-sided configurations (e.g., bolt inserted into a blind tapped hole), only one side of the interface must be accessible. By introducing a constraint interpolation scheme to the fastener access constraint, the optimizer is also allowed to choose the optimum fastener configuration. Finally, a fastener reinforcement constraint ensures sufficient support material exists at each fastener location. The proposed methods are tested on four case studies that demonstrate their effectiveness at creating multi-material topology-optimized designs joined using mechanical fasteners.</p>