The continued success of technology-based companies depends on their proficiency in creating next-generation products and their derivatives. So getting such products out the door on schedule must be routine for such companies, right? Not quite. The authors recently engaged in a detailed study--in which they had access to sensitive internal information and to candid interviews with people at every level--of 28 next-generation product-development projects in 14 leading high-tech companies. They found that most of the companies were unable to complete such projects on schedule. And the companies also had difficulty developing the derivative products needed to fill the gaps in the market that their next-generation products would create. The problem in every case, the authors discovered, was rooted in the product definition phase. And not coincidentally, the successful companies in the study had all learned how to handle the technical and marketplace uncertainties in their product definition processes. The authors have discerned from the actions of those companies a set of best practices that can measurably improve the definition phase of any company's product-development process. They have grouped the techniques into three categories and carefully lay out the steps that companies need to take as they work through each stage. The best practices revealed here are not a magic formula for rapid, successful new-product definition. But they can help companies capture new markets without major delays. And that is good news for any manager facing the uncertainty that goes with developing products for a global marketplace.