|Royal London One-Day Cup|
|Group matches begin on Saturday 26 July and run through to Thursday 21 August|
|Quarter-finals to be played between Tuesday 26 August and Friday 29 August, with semi-finals on Thursday 4 and Saturday 6 September|
|The final will take place at Lord's on Saturday 20 September|
A Roses match between Lancashire and Yorkshire heralds the return of the 50-over format to the county cricket schedule on Saturday.
A 40-over competition has been in place since 2010, but the new One-Day Cup has been launched to bring England into line with international cricket.
The Roses rivals meet at Old Trafford, one of three opening-day games.
Hampshire were the last 50-over champions, beating Sussex in the FP Trophy final at Lord's in 2009.
|Derbyshire||v||Hampshire||26 July, 10:30 BST|
|Glamorgan||v||Middlesex||26 July, 10:30 BST|
|Lancashire||v||Yorkshire||26 July, 14:00 BST|
|Gloucestershire||v||Northamptonshire||27 July, 10:30 BST|
|Leicestershire||v||Derbyshire||27 July, 10:30 BST|
|Middlesex||v||Warwickshire||27 July, 10:30 BST|
|Somerset||v||Durham||27 July, 10:30 BST|
|Sussex||v||Nottinghamshire||27 July, 10:30 BST|
|Worcestershire||v||Essex||27 July, 10:30 BST|
|Surrey||v||Glamorgan||27 July, 11:00 BST|
|Lancashire||v||Hampshire||27 July, 14:00 BST|
Lancashire's Usman Khawaja told BBC Radio Lancashire that batsmen would have to adapt quickly after concentrating on the Championship and T20 cricket so far this summer.
"In the 50-over game, that middle over section is a bit different," the 27-year-old said.
"I think that's one reason why they force you to take a power play in the 34th or 35th over now. It can get a bit mundane.
"The way you progress your innings as a batsman and a batting side changes a little.
"It's a new challenge and that's what they're playing in international cricket, so it makes sense."
Another team in action on the opening day are Hampshire, who travel to Derbyshire.
All-rounder Liam Dawson told BBC Radio Solent he had mixed feelings about the change, but promised that Hampshire would be playing the same aggressive cricket that had served them well in the past.
"I think 40-over cricket was perfect," said the 24-year-old. "Batters always had the licence to try and hit boundaries all the time whereas 50-over cricket can be a little long sometimes and you can get the boring middle bit.
"For batters that like to bat a bit more time, it's a better game for them. Hopefully we don't change our approach to how we play.
"The last few years we've been pretty destructive in 40-over cricket so hopefully we go about it exactly the same way and try to whack it in the first 10 overs."
Glamorgan host Middlesex in the third of Saturday's opening round of fixtures.
The 18 counties are split into two groups of nine with each team playing each other once.
The top four in each group will qualify for the quarter-finals, and the tournament climaxes with the final at Lord's on Saturday, 20 September.
|Royal London One-Day Cup|
|Group A||Group B|
|Lancashire Lightning||Middlesex Panthers|
|Leicestershire Foxes||Nottinghamshire Outlaws|
|Yorkshire Vikings||Sussex Sharks|
|Derbyshire Falcons * (Derbyshire start on -2 after points deduction for a sub-standard pitch in the 2013 season)||Warwickshire|