The U.S. Supreme Court has upheld a lower court order that could release as many as 46,000 inmates in California.
By a vote of 5-4, the court ruled that prison conditions in California are "below standards of decency."
That makes the system run against the standard of cruel and unusual punishment that is mandated by the U.S. Constitution.
California must reduce its inmate population to no more than 110,000.
A panel of three federal judges there will oversee the process.
California could have up to five years to comply.
But dissenting Supreme Court Justices called the decision the "most radical injunction in U.S. History."