This year the deadline falls at 7pm on September 1, with that the cut-off until player trading recommences in the new year.
As ever, it’s been a summer where names have come thick and fast in connection with Pompey.
Some of those reported talks, some have gone on to sign for the Blues with others, well, carrying less substance.
We’ve kept our ears to the ground, so here’s every player linked with Pompey so far - with some insight into the credibility of those reports.
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17. Patrick Nuamah
Nothing in the links with the winger, who has sinced joined Sassuolo after Brescia's collapse - and moved to Serie B side Catanzaro on loan. | Getty Photo: Getty
18. Ronan Hale
Pompey talk wide of the mark over Northern Ireland international who is still with Ross County. Photo: David Maginnis
19. Shandon Baptiste
Mousinho had eyes on his old team-mate, but wages prohibitive for former Premier League midfielder who's been getting minutes with Luton Town. | Getty Images
20. Karl Hein
Pompey talk off the mark for Arsenal keeper who's just joined German side Werder Bremen on loan. | Getty Images