Derby have signed Blackburn goalkeeper Frank Fielding and Sheffield United striker Jamie Ward.
England Under-21 international Fielding has signed a three-year deal, while Ward has put pen to paper on a two-year contract with the option of a further year.
Both players have been on loan at Pride Park this season and complete permanent moves for undisclosed fees.
The Rams have also agreed an undisclosed fee with Championship rivals Millwall for striker Theo Robinson who, like Ward, is set to sign a two-year deal with a year's option.
Robinson will officially join Derby on July 1 after spending the final three months of the season on loan at the club.
"We have stated our desire to keep Frank, Jamie and Theo for some time so it is nice to be in a position now where we can confirm they will be part of our future," said Rams boss Nigel Clough. "All three of them had been on our radar before they even joined us and we've managed to get three of our long-term targets tied down very early in the summer, which is a massive bonus for us we see them all as big parts of our future."