More than 5,000 joint ventures, and many more contractual alliances, have been launched worldwide in the past five years. The largest 100 JVs currently represent more than $350 billion in combined annual revenues. So it’s become clear to many companies that alliances—both equity JVs (where the partners contribute resources to create a new company) and contractual alliances (where the partners collaborate without creating a new company)—can be ideal for managing risk in uncertain markets, sharing the cost of large-scale capital investments, and injecting newfound entrepreneurial spirit into maturing businesses.

A version of this article appeared in the February 2004 issue of Harvard Business Review.