West Brom have completed the signing of Greece international Georgios Samaras on a two-year deal.
Midfielder Henri Lansbury has signed a new three-year deal with Nottingham Forest.
Three years after leaving Stamford Bridge for Benfica, due to a lack of first team opportunities, the 25-year-old midfielder has returned to west London in a £21million deal.
The Serbia international believes he has improved considerably since quitting England in 2011 and is ready to prove himself all over again to a Premier League audience.
He is also fiercely ambitious and is confident that he is re-joining a club that can compete for top honours at home and abroad.
On his targets, both short and long-term, Matic told Chelsea's official website: "First, I want to play and help the team to win the Premier League, and if it's possible to play in and win the Champions League in the future (he is cup-tied in this season's competition).
"I want to win titles here."
Matic is convinced that he can add something to the current Chelsea side, with it his intention to nail down a regular role.
He added: "I've played regularly in a big club at Benfica, where it is not easy and there is a lot of pressure.
"In those years I learned to be a winner and play under that pressure. I developed tactically in Portugal also, training very hard and I believe I am better physically also."
Jose Mourinho played a key role in luring Matic back to England, and he cannot wait to get started under the Portuguese tactician.
Matic said: "We have spoken. He said to be professional, to give my best for the team.
"It's exciting to work with him, he is the best coach in the world and I want to work with him for a long time. I am ready."