As women's football in England evolves, so too does the transfer market.

Among the developments in the Women's Super League have been longer contracts, record transfer fees, release clauses and use of the loan market.

Players are starting to negotiate for better deals and sign-on fees, agents are looking for loopholes in contracts, and clubs want financial security.

Bradley Rains, head of women's football at the CMG Sports agency, told BBC Sport: "Since I've been working in the women’s game, it's changed tremendously.

"When I started, the idea of clubs paying transfer fees in the WSL was a bit of a pipe dream. Now we're seeing that's a lot more common.

"The length and variations of contracts are changing. Clubs are not just shopping in the free market. There's a different attitude. If they have to pay, they will."

Several high-profile players have moved on free transfers already this summer following the expiry of their contracts.

Goalkeeper Mary Earps swapped Manchester United for Paris St-Germain, Vivianne Miedema left Arsenal to join Manchester City, and Fran Kirby signed for Brighton after leaving Chelsea.

But while free transfers have been common in the women's game for years, things are starting to change - albeit gradually.

The transfer fee world record has been broken four times in the past two years.

Zambia forward Racheal Kundananji is the most expensive women's footballer, with National Women's Soccer League side Bay FC having paid £685,000 for her in February.

That beat the record set when England international Keira Walsh moved from Manchester City to Barcelona in 2022 for £400,000.

In June, Liverpool broke their club record by signing Canadian Olivia Smith for £210,000 - five months after Chelsea set a new record for a fee paid by a British team to secure Mayra Ramirez from Levante for more than £400,000.

"Even when you look at clubs with historically smaller budgets in the WSL, they are still paying transfer fees now more often than they ever did," said Rains.

"Bristol City did when they were in the WSL, and West Ham have paid fees for some of the players I have worked with too. It is happening, but it's relative to each club.

"At the top, players leave on free transfers because not many clubs can actually afford them. But they are starting to take a leaf out of the men's game.

"If a club can't afford to pay full whack, players might wait out another year, leave on a free transfer and agree to receive a hefty sell-on bonus payment instead."

More money being exchanged more regularly is not the only change in the game, with many players agreeing to longer contracts.

As well as players having more security, agents have room to negotiate bonuses and clubs have a better investment.

The contracts are also varying. Manchester United, for one, will often add an option-to-extend clause, which means they can keep a player for an extra year.

Some players will ask for clauses that allow them to mutually terminate an agreement if their club are relegated or miss out on Champions League football.

There are also option-to-buy agreements such as when Tottenham made Amanda Nilden's move permanent from Juventus after a successful loan spell.

"It comes down to individual circumstances," said Rains.

"It's interesting how it's becoming more a game of chess than checkers in terms of how moves are plotted.

"It was all the same six or seven years ago. Now, it's a case of trying to manipulate the transfer market in a way that really suits the player-agent model."

Release clauses have long existed in men's football, and these are one of the more intriguing developments in the women's game.

Clubs such as Aston Villa include them in contracts. They mean clubs can guarantee themselves a set amount for the sale of a player - but come with an obvious risk of losing their biggest stars if a clause is triggered.

Villa were caught out in January when Manchester City paid £200,000 for highly rated 20-year-old Laura Blindkilde Brown. It was a fee they did not think would be matched when they agreed her extension two years previously.

This summer, Villa could lose goalkeeper Daphne van Domselaar to Arsenal for the same amount.

But it could represent good business for them - Villa fought off competition to sign Van Domselaar on a free transfer in 2023 and knew there was a chance she could leave before the end of her three-year deal. This ensures they get a good fee.

"Release clauses are a really interesting one," said Rains. "I've just completed a deal for a player where the release clause would make her a world-record transfer.

"Other clubs would realistically never get to that amount of money to buy her. Sometimes these clauses are put in by clubs as a bit of a free hit.

"I would personally steer away from them, but sometimes it's a non-negotiable and you haven't got another option. It might stifle the next move."

The movement of academy graduates has caused consternation outside of the WSL's elite.

Talented young players have been snapped up by the bigger clubs before the age of 18, when they can sign their first professional contract.

Previously, the academy received nothing. Clubs in the top two tiers of English women's football now receive compensation fees - but the feeling is it is not enough.

Brooke Aspin signed for Chelsea in 2023 after leaving Bristol City, who previously lost England internationals Lauren Hemp and Katie Robinson to Manchester City and Brighton respectively.

"It's very hard when that's the landscape and when the big clubs aren't compensating and the rules aren't there," Bristol City chairman Gavin Marshall told BBC Sport in May.

While the system may be detrimental to clubs lower down the pyramid, top WSL sides are benefiting - scouting the best talent and sending them on loan for development.

England midfielder Grace Clinton is one such example. She was signed from Everton's academy by Manchester United, loaned to Tottenham last season and is set to return to United as a fully established international in 2024-25.