Crystal Palace have broken their club transfer record by signing Andros Townsend from Newcastle, while the Magpies have spent big to bolster their chances of promotion from the Championship.
The England international has agreed a five-year contract at the club in a deal believed to be worth £13m, and his transfer comes on the same day Dwight Gayle has moved in the opposite direction.
"I'm extremely delighted," the 24-year-old winger told Palace's official club website.
"I had chats with the manager (Alan Pardew) and chairman (Steve Parish) before I signed and I'm pleased to be part of Crystal Palace's future.
"By the sounds of things it's going to be a bright one and I can't wait to get started."
In becoming Palace's club-record signing - surpassing the £10m spent on Yohan Cabaye last summer - Townsend has moved clubs for the second time in little over six months.
He joined recently-relegated Newcastle for the same fee from Tottenham in January, and his fine form there - he scored four goals in 13 appearances as one of the few players to impress despite their poor season - earned him a call-up to England's initial squad for Euro 2016.
"It's fantastic that we've managed to get a player of Andros' quality into the club," Parish said.
Townsend on the reasons behind his move to #CPFC.
— Crystal Palace F.C. (@CPFC) July 1, 2016
Full video on https://t.co/TTogt72Aro soon! #WelcomeAndros 🔴🔵https://t.co/l6S91a3yFM
Townsend's arrival further strengthens Palace's already strong options in the final third. He is expected to play on either wing, where the talented Wilfried Zaha and Yannick Bolasie are regulars, and where Jason Puncheon also vies for selection.
Also today, the club confirmed the signing of Marseille goalkeeper Steve Mandanda on a three-year contract.
Newcastle meanwhile have confirmed the signing of winger Matt Ritchie from Bournemouth.
Ritchie, 25, has agreed a five-year contract after the two clubs agreed a fee, reported to be around £10m, for the Scotland international.
Rafa Benitez has also added striker Dwight Gayle to his squad with the 25-year-old moving in the opposite direction to Townsend after the clubs agreed a fee in the region of £10m.
Ritchie says he simply couldn't pass up the opportunity to play for the Magpies.
"It's an unbelievable feeling to come to a football club like this," Ritchie told the club's official website.
"I loved it at Bournemouth - I had a fantastic time there and it had a huge impact on my career. But when a club like Newcastle comes calling, I couldn't pass up this opportunity.
"It's fantastic to be here and I'm really looking forward to the challenge of getting the club back in the Premier League."
Bournemouth are understood to have rejected a bid from West Ham last month for Ritchie, who completed his Newcastle medical on Thursday night.
He was a near ever-present for Bournemouth last season, the club's first in the Premier League, scoring four goals in 37 appearances, while he netted 15 for Eddie Howe's side as they won promotion from the Sky Bet Championship in the previous campaign.
Bournemouth paid Swindon £400,000 for Ritchie in January 2013 and he scored 31 goals in a total of 142 appearances for the Dorset club.
Newcastle boss Rafael Benitez added: "We have been following some wingers for a while and Matt was one of the best prospects for this team.
"He has great ability and pace, and as soon as we knew that Andros Townsend could be leaving, our priority was to finalise this deal.
"We have signed an exciting winger who has experience in the Championship but has also proved that he can step up to the top level. I am delighted that he is now part of our squad."
Ritchie is Newcastle's third summer signing following the arrival of Gayle and goalkeeper Matz Sels, signed from Belgian side Gent for a reported fee of £4.5m.
