Pompey so far have brought in two players – Sean Raggett and Cameron Pring - ahead of a renewed promotion push.
Meanwhile, the likes of Peterborough, Sunderland, Charlton and Hull have also been improving their sides as they push for the Championship.
But what about the players that clubs have lost? The departures of key men can often prove detrimental to teams' ambitions.
Scroll down and click through the pages to see who each side will miss...
1. Accrington
Flying winger Jordan Clark turned down a new contract and signed for Championship Luton. Goalkeeper Dimitar Evtimov has also left for CSKA Sofia. Photo: Charlotte Tattersall
2. AFC Wimbledon
Goalkeeper Nathan Trott impressed during his season-long loan from West Ham. Experienced-midfielder Scott Wagstaff has also left for Forest Green. Photo: Malcolm Mackenzie
3. Blackpool
Manager Neil Critchley has had a huge clearout this summer, but one player they might miss is Armand Gnanduillet. The striker netted 18 times for the Seasiders last season. Photo: .
4. Bristol Rovers
Prolific marksman Jonson Clarke-Harris has departed the Memorial Stadium. He netted 27 goals in 49 appearances for Rovers during his one-and-a-half years at the club. Photo: .