Pompey have signed striker Joe Pigott from Ipswich on a season-long loan deal.
Marcus Harness heads in the opposite direction, joining the Tractor Boys permanently for an undisclosed fee.
Pigott previously appeared for Charlton, Cambridge and Maidstone before moving to AFC Wimbledon in January 2018.
He netted 54 times in 157 appearances for the club – including the first goal scored at the new Plough Lane.
Dons fans named Pigott their Player of the Year for the 2020/21 campaign before he departed for Ipswich.
Blues boss Danny Cowley said: “We’ve got a player who is really hungry – he loves football and was starved of that a bit last season.
“So he’s highly motivated and was eager to come to Pompey, where he’s previously scored a few goals.
“Joe previously went back into non-league football with Maidstone, where he had a great record to earn his move to AFC Wimbledon.
“Simon Bassey worked with him there and they have a good relationship. He’s a boy we know really well.
“Joe will bring some real intelligence and good link play, while he obviously carries a threat in the final third.
“He's an excellent finisher with both feet and scores all kinds of goals, making clever runs behind defenders.
“We’re pleased to have Joe and I think we’ve signed him at exactly the right time. We’re really looking forward to working with him.”
Harness departs Fratton Park having struck 31 times in 134 matches during his three years with Pompey, which included a hat-trick at former club Burton in October 2020.
His best run of form arrived midway through last season, with the forward finding the net on eight occasions in a run of just 12 games.
Cowley said: “We’re sad to say goodbye to Marcus, who was a key player for us last season – both with his goals and assists.
“He’s someone who I think has Championship quality, but ultimately it was the right time for him to move on.
“And with only a year left on his contract, it makes good business sense for us and gives us some flexibility in further developing our squad.
“I’m sure all our supporters will join me in wishing Marcus the very best for his career and we appreciate his efforts in a Pompey shirt.”
