Marriott has acquired Starwood, and on day one they’re already making it possible to link frequent guest accounts, match status, and transfer points between programs.
Marriott and Starwood are still separate, the programs are still independent — you earn and redeem Starwood points at Sheraton, Westin, etc. and you earn and redeem Marriott points at Marriott, Renaissance, etc. — but you can move your points back and forth and elite customers of one can be treated as elites with both.