Traditionally, software-intensive systems have been acquired, developed, tested, and maintained as separate products, even if these systems have a significant amount of common functionality and code. Such an approach wastes technical resources, takes longer, and costs more than necessary. A product line approach to software can reduce development cycles, improve return on software investments, improve software system integration, and give an organization more future options. Building a new product or system becomes more a matter of assembly or generation than creation, of integration rather than programming. Organizations of all types and sizes are discovering that a product line strategy, when skillfully implemented, can improve productivity, quality, and time to market. Software product lines present at long last a reuse strategy with real economic benefit.