Derbyshire
Ins: Zak Chappell (Nottinghamshire), Matthew Lamb (Warwickshire), Mark Watt
Outs: Dustin Melton, Mikey Cohen (released), Alex Hughes (retired)
Overseas players: Suranga Lakmal (Sri Lanka), Haider Ali (Pakistan)
Durham
Ins: Ollie Robinson (Kent), Nathan Sowter (Middlesex), Brandon Glover (Northamptonshire), Bas de Leede
Outs: Chris Rushworth (Warwickshire), Sean Dickson (Somerset), Matt Salisbury (Leicestershire), Ned Eckersley (released)
Overseas players: David Bedingham (South Africa), Tristan Stubbs (South Africa - Vitality Blast)
Essex
Overseas players: Simon Harmer (South Africa), Will Sutherland (Australia - County Championship, until the end of July), Daniel Sams (Australia - Vitality Blast)
Ins: None
Outs: Adam Wheater (retired), Jack Plom (released)
Glamorgan
Ins: Harry Podmore (Kent), Zain-ul-Hassan (South Asian Cricket Academy)
Outs: Michael Hogan (Kent), Lukas Carey, Joe Cooke, Tom Cullen, Ruaidhri Smith, James Weighell, Tegid Phillips (all released)
Overseas players: Marnus Labuschagne (Australia), Michael Neser (Australia), Colin Ingram (South Africa)
Gloucestershire
Ins: Marchant de Lange (Somerset)
Outs: Ryan Higgins (Middlesex), Benny Howell (Hampshire), Ian ****bain (released)
Overseas players: Marcus Harris (Australia), Zafar Gohar (Pakistan)
Hampshire
Ins: Benny Howell (Gloucestershire)
Outs: Lewis McManus (Northamptonshire)
Overseas players: Kyle Abbott (South Africa), Mohammad Abbas (Pakistan), Ben McDermott (Australia - Vitality Blast), Nathan Ellis (Australia - Vitality Blast)
Kent
Ins: Joey Evison (Nottinghamshire), Michael Hogan (Glamorgan)
Outs: Ollie Robinson (Durham), Matt Milnes (Yorkshire), Harry Podmore (Glamorgan), Darren Stevens (released)
Overseas players: Arshdeep Singh (India - five County Championship matches across June and July), Kane Richardson (Australia - Vitality Blast)
Lancashire
Ins: None
Outs: Liam Hurt (released)
Overseas players: Dane Vilas (South Africa), Daryl Mitchell (New Zealand), Colin de Grandhomme (New Zealand)
Leicestershire
Ins: Sol Budinger (Nottinghamshire), Matt Salisbury (Durham)
Outs: Ben Mike (Yorkshire), Hassan Azad, Sam Bates, Nat Bowley, Alex Evans, Gareth Griffiths, Abi Sakande (all released)
Overseas players: Wiaan Mulder (South Africa), Peter Handscomb (Australia - County Championship, April and May), Ajinkya Rahane (India - County Championship and One-Day Cup, June onwards), Naveen-ul-Haq (Afghanistan - Vitality Blast)
Middlesex
Ins: Ryan Higgins (Gloucestershire)
Outs: Nathan Sowter (Durham)
Overseas players: Pieter Malan (South Africa)
Northamptonshire
Ins: David Willey (Yorkshire), Lewis McManus (Hampshire), Ollie Sale (Somerset)
Outs: Brandon Glover (Durham), Nathan Buck (retired), Charlie Thurston, Ben Curran (both released)
Overseas players: Chris Lynn (Australia - Vitality Blast), AJ Tye (Australia - Vitality Blast), Sam Whiteman (Australia - County Championship and One-Day Cup, until the end of August)
Nottinghamshire
Ins: Olly Stone (Warwickshire), Tom Loten (Yorkshire)
Outs: Joey Evison (Kent), Zak Chappell (Derbyshire), Sol Budinger (Leicestershire)
Overseas players: Dane Paterson (South Africa), Colin Munro (New Zealand - Vitality Blast)
Somerset
Ins: Tom Kohler-Cadmore (Yorkshire), Sean Dickson (Durham), Shoaib Bashir (Berkshire)
Outs: Marchant de Lange (Gloucestershire), Ollie Sale (Northamptonshire), James Hildreth, Max Waller (both retired)
Overseas players: Peter Siddle (Australia - County Championship and Vitality Blast, until the end of July) Matt Henry (New Zealand - County Championship and Vitality Blast)
Surrey
Ins: Dom Sibley (Warwickshire)
Outs: Hashim Amla (retired)
Overseas players: Kemar Roach (West Indies - first six rounds of County Championship), Sean Abbott (Australia - County Championship and Vitality Blast, until the end of July), Sunil Narine (West Indies - Vitality Blast)
Sussex
Ins: Tom Alsop (Hampshire)
Outs: Luke Wright (retired)
Overseas players: Steve Smith (Australia - three County Championship games in May), Cheteshwar Pujara (India), Shadab Khan (Pakistan - Vitality Blast), Nathan McAndrew (Australia - April to July, County Championship and Vitality Blast)
Warwickshire
Ins: Moeen Ali (Worcestershire), Ed Barnard (Worcestershire), Chris Rushworth (Durham)
Outs: Dom Sibley (Surrey), Olly Stone (Nottinghamshire), Adam Hose (Worcestershire), Matthew Lamb (Derbyshire), Ryan Sidebottom (released)
Overseas players: Hassan Ali (Pakistan - until the end of July), Glenn Maxwell (Australia - Vitality Blast)
Worcestershire
Ins: Adam Hose (Warwickshire), Matthew Waite (Yorkshire)
Outs: Moeen Ali (Warwickshire), Ed Barnard (Warwickshire), Tom Fell, Josh Dell, Jacques Banton (all released)
Overseas players: Azhar Ali (Pakistan), Michael Bracewell (New Zealand - Vitality Blast), Mitchell Santner (New Zealand - Vitality Blast)
Yorkshire
Ins: Matt Milnes (Kent), Ben Mike (Leicestershire), Jafer Chohan (South Asian Cricket Academy)
Outs: Gary Ballance (released, will now play for Zimbabwe), David Willey (Northamptonshire), Tom Kohler-Cadmore (Somerset), Matthew Waite (Worcestershire), Tom Loten (Nottinghamshire), Steve Patterson (retired), Harry Sullivan, Josh Sullivan (both released)
Overseas players: Shan Masood (Pakistan), Neil Wagner (New Zealand - first 10 County Championship matches), David Wiese (Namibia - Vitality Blast)