Sidwell turned down a new contract with Reading despite helping the club finish eighth in its first ever Premier League season.
Chelsea said he passed a medical exam Tuesday.
The Blues need backup in midfield this season as several players will be taking part in the Jan. 20-Feb. 10 African Cup of Nations - notably Ghana's Michael Essien and Nigeria's John Obi Mikel.
Sidwell was a trainee with Arsenal, and was loaned to Brentford, Beveren and Brighton before he joined Reading in 2003. He helped the club get promoted to the Premier League in 2006.
Russia has been developing an energy module on the basis of the megawatt-class nuclear power plant since 2010. The spaceship needs neither sunlight nor solar batteries
There are legitimate authorities in Donetsk and Luhansk republics now, with which Russia can implement the project of the economic integration of the Donbass
Austria does not intend to expel Russian diplomats because of the spy scandal