To cope with the challenges of market competition and the greater purchasing power of consumers, manufacturers have increased the variety of products they offer. Product families and reconfigurable manufacturing systems (RMS) are used to produce product variety cost-effectively. However, there is a lack of concurrent engineering methods for the joint design of a product family and an RMS, since existing concurrent engineering methods were developed for a single product and its associated manufacturing system. The presence of product variety brings challenges to the concurrent engineering of a product family and its reconfigurable assembly system (RAS), as the decision space is broader. This paper introduces a mathematical model for the concurrent design of a product family and a RAS. In addition, a mathematical model for the sequential approach to product family and RAS design is introduced to compare with the results of the concurrent methodology. A genetic algorithm has been developed to solve the models introduced for both the concurrent and sequential approaches. Examples are used to demonstrate the implementation of the concurrent approach to product family and RAS design and the benefits that could be achieved by using this approach. The solutions indicate that the concurrent design of product families and RASs leads to profits that are the same as or higher than the profits obtained with the sequential design approach. Therefore, the concurrent design of product families and RAS methodology is a more cost-effective approach to designing families of products and their associated manufacturing systems.