For more than two decades, New York City's five organized-crime families were plagued by convictions brought on by strengthened federal laws and the increasing habit of higher-ranking members cooperating with the government.

Those years of high-profile decline created a perception that the city's mafia is on the verge of extinction. But law-enforcement officials and mob experts say the five families, while not the force they once were, are far from sleeping with the fishes. They have survived, the experts said, because of...