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...
9. Hull
Hull have made some decent signings this summer, but also lost some key players. Herbie Kane, once on Pompey's radar, is back at Liverpool after his loan spell. Midfielder Kevin Stewart has departed the Tigers and centre-half Ryan Tafazolli joined Wycombe for an undisclosed fee earlier this week. Photo: .
10. Fleetwood
Harry Souttar has been a rock in Fleetwood's defence for the past two seasons but has now returned to Stoke after his loan. Likewise, Everton duo Lewis Gibson and Callum Connolly are back at Goodison Park. The Cod Army have also sold right-back Lewie Coyle to Hull. Photo: .
11. Gillingham
Steve Evans had a huge clearout at Priestfield this summer. He wanted to keep captain Max Ehmer, but he chose to join Bristol Rovers. The Gills may also see striker Brandon Hanlan depart. Pompey have been keen but Evans reckons Kenny Jackett's interest has now cooled. Photo: .
12. Ipswich
Ipswich haven't suffered wholesale changes this summer, although Paul Lambert will be sad to see Luke Garbutt depart after his season-long loan. Crystal Palace are interested in midfielder Flynn Downes, having had bids rejected. Photo: Graham Hunt