The proliferation of new products has become a common phenomenon in today's business world. Most companies now offer hundreds, if not thousands, of stock keeping units (SKUs) in order to compete in the market place. Companies that expand their product and service varieties now face a new set of problems: accurate demand forecasts, controlling production and inventory costs, and providing high quality delivery performance. In addition, marketing managers will often advocate widening product lines for increasing revenue and market share, but increasing product lines can also decrease the efficiency of manufacturing processes and distribution systems. Hence, firms must weigh the benefits of increasing product variety against its cost and determine the optimal level of product variety to offer to their customers. This text examines the interrelated problems between the marketing and production functions in industry, and through a series of research survey papers by leading scholars in economics, engineering, marketing, and operations research, the book addresses the following questions: Why do companies extend their product lines? Do consumers care about product variety? Will a brand with more variety enjoy higher market share? How should product variety be measured? How can a company exploit its product and process design to deliver a higher level of product variety quickly and cheaply? What should the level of product variety be and what should the price of each of the product variants be? What kind of challenges would a company face in offering a high level of product variety and how can these obstacles be overcome? The solutions to these questions are drawn from multiple functions and a variety of disciplines.