| 25 Aug 17 | R. Snodgrass Robert Snodgrass |  West Ham UnitedWHU | → |  Aston VillaAVL | Loan |
| 25 Aug 17 | R. Snodgrass Robert Snodgrass | West Ham UnitedWHU | → | Aston VillaAVL | Loan |
| 14 Aug 17 | S. Feghouli Sofiane Feghouli | West Ham UnitedWHU | → |  GalatasarayGAL | 3860000 |
| 07 Aug 17 | S. Haksabanovic Sead Haksabanovic |  Halmstads BKHBK | → | West Ham UnitedWHU | Undisclosed |
| 02 Aug 17 | K. Knoyle Kyle Knoyle | West Ham UnitedWHU | → |  Swindon TownSWI | Free |
| 01 Aug 17 | R. Burke Reece Burke | West Ham UnitedWHU | → |  Bolton WanderersBOL | Loan |
| 01 Aug 17 | J. Cullen Josh Cullen | West Ham UnitedWHU | → | Bolton WanderersBOL | Loan |
| 01 Aug 17 | R. Burke Reece Burke | West Ham UnitedWHU | → | Bolton WanderersBOL | Loan |
| 01 Aug 17 | J. Cullen Josh Cullen | West Ham UnitedWHU | → | Bolton WanderersBOL | Loan |
| 28 Jul 17 | A. Fletcher Ashley Fletcher | West Ham UnitedWHU | → |  MiddlesbroughMID | 6,500,000 |
| 28 Jul 17 | A. Fletcher Ashley Fletcher | West Ham UnitedWHU | → | MiddlesbroughMID | 6,500,000 |
| 24 Jul 17 | J. Hernández Javier Hernández |  Bayer LeverkusenLEV | → | West Ham UnitedWHU | 16000000 |
| 24 Jul 17 | J. Hernández Javier Hernández | Bayer LeverkusenLEV | → | West Ham UnitedWHU | 16000000 |
| 22 Jul 17 | D. Randolph Darren Randolph | West Ham UnitedWHU | → | MiddlesbroughMID | 5,000,000 |
| 22 Jul 17 | M. Arnautovic Marko Arnautovic |  Stoke CitySTK | → | West Ham UnitedWHU | Undisclosed |
| 22 Jul 17 | D. Randolph Darren Randolph | West Ham UnitedWHU | → | MiddlesbroughMID | 5,000,000 |
| 18 Jul 17 | J. Hart Joe Hart |  Manchester CityMNC | → | West Ham UnitedWHU | Loan |
| 16 Jul 17 | G. Dobson George Dobson | West Ham UnitedWHU | → |  Sparta RotterdamSPA | Undisclosed |
| 16 Jul 17 | G. Dobson George Dobson | West Ham UnitedWHU | → | Sparta RotterdamSPA | Undisclosed |
| 13 Jul 17 | E. Valencia Enner Valencia | West Ham UnitedWHU | → |  Tigres UANLUANL | Undisclosed |
| 13 Jul 17 | E. Valencia Enner Valencia | West Ham UnitedWHU | → | Tigres UANLUANL | Undisclosed |
| 01 Jul 17 | P. Zabaleta Pablo Zabaleta | Manchester CityMNC | → | West Ham UnitedWHU | Free |
| 01 Jul 17 | H. Nordtveit Håvard Nordtveit | West Ham UnitedWHU | → |  TSG HoffenheimHOF | Undisclosed |
| 01 Jul 17 | H. Nordtveit Håvard Nordtveit | West Ham UnitedWHU | → | TSG HoffenheimHOF | Undisclosed |
| 01 Jul 17 | R. Oxford Reece Oxford | West Ham UnitedWHU | → |  Borussia MonchengladbachMON | Loan |
| 01 Jul 17 | R. Oxford Reece Oxford | West Ham UnitedWHU | → | Borussia MonchengladbachMON | Loan |
| 31 Jan 17 | R. Oxford Reece Oxford | West Ham UnitedWHU | → |  ReadingREA | Loan |
| 31 Jan 17 | R. Oxford Reece Oxford | West Ham UnitedWHU | → | ReadingREA | Loan |
| 29 Jan 17 | D. Payet Dimitri Payet | West Ham UnitedWHU | → |  MarseilleMAR | 25000000 |
| 29 Jan 17 | D. Payet Dimitri Payet | West Ham UnitedWHU | → | MarseilleMAR | 25000000 |
| 27 Jan 17 | R. Snodgrass Robert Snodgrass |  Hull CityHUL | → | West Ham UnitedWHU | 10200000 |
| 23 Jan 17 | Toni Martinez | West Ham UnitedWHU | → |  Oxford UnitedOXF | Loan |
| 22 Jan 17 | N. Holland Nathan Holland |  EvertonEVE | → | West Ham UnitedWHU | Undisclosed |
| 20 Jan 17 | M. Browne Marcus Browne | West Ham UnitedWHU | → |  Wigan AthleticWGA | Loan |
| 20 Jan 17 | J. Fonte José Fonte |  SouthamptonSOU | → | West Ham UnitedWHU | Undisclosed |
| 20 Jan 17 | M. Browne Marcus Browne | West Ham UnitedWHU | → | Wigan AthleticWGA | Loan |
| 12 Jan 17 | A. Pike Alex Pike | West Ham UnitedWHU | → |  Cheltenham TownCHL | Loan |
| 06 Jan 17 | L. Page Lewis Page | West Ham UnitedWHU | → |  Charlton AthleticCHA | Undisclosed |
| 01 Jan 17 | M. Samuelsen Martin Samuelsen | West Ham UnitedWHU | → |  Peterborough UnitedPET | Loan |
| 01 Jan 17 | J. Gordon Jaanai Gordon | West Ham UnitedWHU | → |  Newport CountyNEW | Loan |