French right back Jean Yves Anis was signed from Rennes, Mauro Oscar Coelho Da Silva from Porto and Mbark Boussoufa signs from Ajax. The latter two are both 18, whilst Anis is slightly older at 21.
All three were out of contract and join on a free tranfer. Chelsea secretary David Barnard said: "These three boys are ones for the future. They were earmarked by our system.
"They were out of contract at their clubs and the opportunity came up to sign them.''
According to Football365.com, Da Silva's signing came after the youngster had a disagreement with a coach at Porto. Amadeu Paixco said, "Da Silva had been at Porto for seven years.
"He'd been there since he was 11 - but they had seven centre-halves of the same age so had to offload some.
"Porto's sporting director liked him - but one of the junior coaches didn't.
"Maybe that's just one of those things, but it's a lucky thing for Chelsea.
"He was a free agent so went on trial to Chelsea for two weeks last month. They liked him and kept him.''