The former Reading midfielder is a free transfer.
In their classic ham-fisted way, Chelsea have revealed no other details - ie the length of the deal, etc.
So here goes, the 24-year-old is believed to have signed a four-year-deal which will probably be but, not much more than the £25k per week deal offered by Reading for him to stay.
Sidwell was an Arsenal trainee before being farmed out on loan Brentford and then was offloaded to Brevern and Brighton before signing for Steve Coppell's Reading in January 2003.
This no-cost player will be joining the mega-buck, multi-international Chelsea on July 1.
He scored four times in 35 Premiership matches last season.
Good luck Steve or Steven, you are going to need it.