The legal world hasn’t always been known for its friendliness to females; the number of women general counsels in the Fortune 500 topped out at 94 in 2010. But at several current and former Fortune 500 companies—Gap Inc., Pitney Bowes, Cummins and CIGNA—female general counsels have been the rule, not the exception, for the past decade. At all four businesses, at least three consecutive women have held the general counsel spot.

Project 5/165 co-founder and former Fortune 500 GC Anastasia Kelly, who aims to see 165 female general counsels in the Fortune 500, points to several essential steps that can help other companies repeat this success.

One key component of success is networking, both inside a company and within the broader general counsel and law firm communities. “Even though the project is geared at women general counsels,” Kelly said, “the numbers are just as pitiful in law firms when it comes to being in the top tier of the partnership.” She hopes that an open discussion of women’s advancement in the legal community will lead to more “planned, conscious” change.

A second crucial factor is ensuring that women are being hired into entry-level and mid-level positions, not just executive posts, as promoting women to the higher echelons requires having strong female representation at all levels. “It would be interesting to look at those companies and see what bench strength they had in terms of females,” Kelly noted.

Once a woman reaches the general counsel spot, she can then draw on that bench strength to ensure that other women follow in her footsteps. “If a female general counsel is retiring or leaving amicably, would she be helping to name her successor?” Kelly asked. “And would that help her to name a woman as her successor?”

That seems to be the case at these four companies, where outgoing female GCs have often hand-picked their successors. When Anne Gust Brown left Gap Inc., for instance, she chose mentee Lauri Shanahan to replace her. In turn, Shanahan personally selected Michelle Banks as her successor when Shanahan resigned as GC eight years later. A similar pattern of succession has emerged at Pitney Bowes, where departing general counsel Sara Moss knew in advance who she wanted to assume the position next: She chose Michele Coleman Mayes, who had once pitched business to Pitney Bowes as a law firm partner. Moss was so sure of her decision that she told then CEO Mike Critelli not to advertise the general counsel position, according to the book “Courageous Counsel”.

Kelly sees this pattern as key to continuing women’s success throughout the legal community: “Once a woman cracks that glass ceiling it’s just easier for more women to do that.”