Sir Win Bischoff didn't hesitate to sign on. The chairman of Lloyds Banking Group was one of the first men asked to join The 30% Club, a London-based group whose mission is to boost the ratio of women on U.K. corporate boards to 30 percent by 2016.

With female directors still woefully outnumbered by men despite decades of advocacy, Bischoff says strong action is necessary. "It takes a diversity of views to make sure you get to the correct view, and women can help you achieve that diversity," says Bischoff, whose own board is 13 percent female—with two women out of 15 directors.

However, he concedes that the initiative is entirely voluntary, and in that sense not very different from similar programs launched in the past. "This is not obligatory. This is aspirational," he says. "We're trying to set a good example."

The group, which launched in November, consists of chairmen from some of Britain's largest companies who have vowed to achieve the 30 percent goal within their own companies and to get other chairmen to join in the effort.

Helena Morrissey, chief executive of Newton Investment Management, the British arm of BNY Mellon Asset Management, launched The 30% Club after becoming frustrated with what she views as a lack of progress in getting more women on corporate boards.

Besides Bischoff, chairmen that have joined include Lord Sharman of Redlynch, chairman of insurance giant Aviva; Roger Carr, chairman of the energy company Centrica; and David Tyler, chairman of Sainsbury's.

Morrissey says the organization plans to enlist a second round of chairmen later this year.

The group has framed its cause as a competitive concern, citing growing evidence that women help boards to govern more effectively.

"This is not a feminist issue, this is a business issue," says Angela Knight, CEO of the British Bankers' Association, which has formally backed the initiative. "If boards all look the same, will they end up making the same kinds of decisions? After the banking crisis, the question was asked whether there would have been so much groupthink if there had been a broader representation on boards."

In 2010, women made up only 7.9 percent of board members in the U.K.'s Financial Times Stock Exchange 250 companies, according to research by Catalyst, a nonprofit dedicated to workplace diversity.

In the U.S., the numbers are better, but not significantly so. Women make up 15.7 percent of Fortune 500 directors. In the financial sector, they make up 16.8 percent, according to Catalyst.

Studies indicate that gender diversity is good for business. For example, companies in the top quartile for female representation on the board have a 53 percent higher return on equity than companies in the bottom quartile, according to Catalyst.

Morrissey says the launch of The 30% Club is timely, considering that France, Spain, Norway and The Netherlands have all passed quotas regarding gender diversity on corporate boards. In France, for example, the parliament passed a law in January requiring large companies—those which are either publicly traded, have more than 500 employees or revenues above 50 million euros—to ensure that at least 40 percent of their board directors are women.

The European Union is considering cross-border laws as well. "We're facing a lot of political pressure from continental Europe," Morrissey says.

The prospect of quotas in the United Kingdom is a growing concern. In August, the British government asked Lord Mervyn Davies, former trade and investment minister and now a member of the House of Lords, to examine the issue and recommend fixes. He was due to submit a report in February.

Not everyone views quotas as a benefit to women. Irene Dorner, CEO of HSBC USA, says that quotas hurt women by implying they wouldn't have been able to gain positions of power on their merit. "You can't change the world by injecting a quota at the top of an organization," she says. "You have to build an organization on a meritocracy basis, and create an environment where women can come through an organization and prepare themselves to become board members."

Dorner is one of two women on the seven-member board of HSBC Bank USA, and one of four women on the 12-member board of HSBC North America. She was appointed to the boards in January of last year when she became CEO.

In the United States, quotas seem unlikely, but the issue of board diversity is gaining momentum. Last year, the Securities and Exchange Commission issued new rules requiring companies to tell shareholders how diversity factored into their director nominations.

Eileen Kamerick, a director at Associated Banc-Corp. in Green Bay, Wis., and the chief financial officer at Houlihan Lokey, a New York investment firm, says the SEC's new rule and other recent reforms will help advance the cause. For example, the Dodd-Frank Act, which holds boards accountable for the actions of the companies they govern, is requiring boards to nominate members with specialized skills.

"The fact that you need someone who is a financial expert and can follow a five-hour auditing committee report means you have to cast a broader net for directors. That gives women more opportunities," Kamerick says. So, where in the past companies might have sought board members largely for their CEO experience—which inevitably ruled out many women as the vast majority of CEOs are male—they might now be inclined to seek someone with experience as an auditor or chief financial officer.

American efforts around diversity have mostly been led by nonprofit organizations or groups of female advocates that offer educational and networking opportunities and seek to influence the public debate.

Susan Stautberg, founder of Women Corporate Directors, one of the U.S.'s largest organizations focused on corporate gender diversity, says that it has been successful in promoting its databank of women qualified to fill board and C-level positions and in advocating to make sure women are invited to speak at professional events across all industries.

A newer nonprofit, Boston-based 2020 Women on Boards, has a mission to ensure that women make up 20 percent of board members by 2020. It was founded by Stephanie Sonnabend, CEO of Sonesta Hotels, who serves on the board of Century Bank in Medford, Mass. The campaign seeks to build public awareness and next year plans to distribute to the media a nationwide ranking of companies based on the participation of women on their boards. Sonnabend sees potential for rapid progress once more people become aware of the issue.

"The green movement has been around for 40 years, but it's only taken off in the last five years because consumers have started to ask businesses questions"— like whether hotels recycle, conserve energy or source food locally, says Sonnabend. "If people realized that women make up such a small percentage of boards, they'd be concerned."

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