Meet the new policemen of U.S. corporate governance: the nation’s judges.

Like it or not, shareholder activism to exert control over board behavior is migrating as never before to courtrooms, giving magistrates and juries unusual sway over how companies are run. Canny executives can take steps to avoid getting into plaintiff lawyers’ sites. But first, take a quick scan of the landscape unfolding in 2006.

Enron’s trial, of course, has grabbed headlines. So has its civil suit. But in its shadow are other mega-cases, the latest being Nortel Networks, the Canadian telecommunications firm. Earlier this year, management settled a class ...