Harlequins have secured the services of Leicester Tigers flanker Will Evans and locks Stephan Lewies and Glen Young for the 2019-20 season.
Evans has spent his entire senior career so far at Welford Road and, when making his debut in 2016 at the age of 19 years and 64 days, he became the club's second-youngest Premiership player.
The 22-year-old has played for England at four junior levels and was part of the team which made it to the final of the World U20 Championship in 2017.
Evans said: "There is a great buzz around Harlequins at the moment and I know they are an incredibly ambitious club.
"I know Gussy [head of rugby Paul Gustard] and his team are hungry for trophies and I look forward to being part of that group, learning from them to improve my own game and helping the squad achieve its ambitions."
Gustard added: "Will is a player I have been fortunate to work with before.
"He is a young man with a very clear goal of where he wants to get to and we are delighted he has chosen to join us as he takes the next step forward in his burgeoning career.
"He is a tough-on-the-ball No 7, he tackles hard and runs with real intent. He is a super talent and I am confident in our ability to help him develop his game, fulfil his potential and realise his ambitions, which in turn will help us achieve ours."
Lewies, who currently on loan at Super Rugby side Lions in from Sharks, is a South Africa A international and was called up to the senior Springbok squad for the Test against Scotland in Port Elizabeth in 2014.
He said: "This is a very exciting time for me, to be joining a club with such a great history and standing in English rugby, but also one that is on a new journey with a new head of rugby who, like me, is incredibly ambitious.
"I am coming to Harlequins to win things and I look forward to getting started next season."
Young has only played twice in the Premiership for Dean Richards' Newcastle Falcons but has been involved in their Champions Cup campaign.
Gustard added: "Glen is an incredibly promising talent and we are looking forward to having him as part of our squad as we look to build on the early momentum we have earned to date,
"He is hungry, energetic and is desperate to improve. He loves line-outs and will add real awareness and acumen to our calling systems and structures."