No one was betting on Renault Chief Executive Louis Schweitzer when he boldly paid $6 billion in 1999 for a 36.8% stake in troubled Nissan Motor Co. in 1999. Experts insisted the effort to turn around the nearly insolvent Japanese company would sink Renault--and Schweitzer. But the alliance has transformed Renault into a serious global challenger and propelled revenues and profits at both companies. Despite a shrinking market in 2003, Renault managed to boost revenues 3%. Net income jumped 27%, with Nissan contributing almost half of the increase. Schweitzer's genius was avoiding the potential pitfalls of a takeover while reaping the benefits of higher-volume production on shared platforms. Renault helped Nissan revamp a tired product lineup. Now Nissan is helping infuse the style-savvy French auto maker with first-class production technology. Thanks to the successful rollout of Renault's second-generation versions of its flagship Mégane sedans and Scénic minivans last year, Renault defended its title as Europe's No.1 brand, outselling Volkswagen for two years in a row. This month it introduced the Logan, a $6,000 mini car produced in Romania for emerging markets. Schweitzer plans to hand off leadership of Renault to Nissan CEO Carlos Ghosn in 2005. But this French executive is convinced Renault hasn't even hit cruising speed.