During the past 50-odd years, the North American legal profession has been notable for a ready supply of labour. The post-war population boom and increased access to post-secondary education, combined with the enduring lure of a legal career, ensured that there would always be a deep pool of lawyers into which firms could dip for talent.

When a buyer’s market lasts that long, the buyers’ advantages become locked into the prevailing culture of the marketplace. Much of what we take for granted in modern law firms — hourly billable targets, ever-increasing workloads, lengthening partnership tracks, client hoarding by partners, and more — can be traced at least in part to firms’ established ability to dictate the terms of employment to a fairly low-cost and easily leveraged labour pool. Law firm employers have held the whip hand for so long that we’ve come to think it’s just the natural order of things.

That’s about to change. Talent — in nicer terms, the actual human beings who provide legal services — is becoming scarce. This is new, and for a lot of law firms, it’s not going to be fun.

Obviously, part of it is that demographics giveth and demographics taketh away. The great Boomer exodus from the workforce isn’t unfolding as dramatically as some predicted, but the legal recruiters I’ve talked with say it’s a real issue.

It’s not so much that the Boomer partners have reached “retirement age” — I think this generation will stay fully occupied at one thing or another till the day they drop — but that many of them won’t be enticed to keep plugging away at the firm. They’re financially comfortable, their kids have grown, and they want to travel, or start a vineyard, or become full-time directors, or give back to their communities, or do something other than show up at the office again this week. One way or another, their numbers will start dropping faster than age-related attrition would suggest.

At the other end, the Millennials are now entering the profession. Enough has been published about the workplace impact of Generation Y to choke a horse, but the key takeaway here is that members of this cohort believe they have many more options than the two generations that came before it. They’ve never experienced a recession, they’ve always been able to count on financial backup from their parents, and they’ve never been given a reason to live by any terms but their own.

In short, they’re natural-born sellers — and by a happy coincidence, they’re entering the first seller’s market the legal profession has seen in decades. This is already discombobulating a lot of partnership committees that aren’t used to hearing current or prospective employees talk and behave like this.

But it’s not just that this group has a different attitude towards work. It’s also a different marketplace for talent out there.

The new economy is providing scores of new career paths for people with legal backgrounds. Many of these paths offer more interesting work in more exciting industries for more money than the law can provide (notice how “fewer hours,” the supposed Achilles’ heel of these supposedly uncommitted youngsters, isn’t on that list?). One of the reasons New York law firms had to raise first-year lawyer salaries to $160,000 a year was that investment banks and hedge funds, cutting-edge employers for whom money truly is no object, were snapping up the top law grads. This won’t be confined to the Big Apple. Law firms all over the continent are going to find it increasingly hard to compete with other employers who can offer lawyers interesting work at a good salary.

Many firms faced with this problem are going to try solving it the old-fashioned way: throwing money at it. That doesn’t work terribly well at the moment, and it’s going to work less well in future, because the truly fatal characteristic of many law firm jobs isn’t the money or even the hours or the pressure — it’s that the quality of the work isn’t all that great.

What a lot of law firm associates are quietly saying is that the type of work they typically receive is distinguished largely by drudgery and routine. Younger lawyers aren’t afraid of working hard, but they have a heartfelt aversion to working hard at mundane tasks for years on end without an excellent reason for doing so. These lawyers want to do interesting work, learn new skills, and improve their networks in a congenial atmosphere. And they’ll go to the wall for employers who offer it.

But many law firm partners still keep most of the good work and client contact to themselves. And no one has ever accused your average law firm of being an upbeat, can-do workplace. When there were lots of lawyers around who didn’t feel they had many other career choices — and who were a lot more interested in gaining equity partnership status than this current group is — firms could get away with that kind of stuff. Now, not so much. The resounding message many younger lawyers have been sending firms the last few years is that life in a law firm is not, as they say, all that and a bag of chips.

So, what do we have? The departure of older Boomers is set to accelerate, and the influx of newer Millennials is going to be diluted. In the result, there will be fewer lawyers available to take on the available work, which should mean these lawyers can demand higher wages and other concessions from their firms. This will come at a particularly bad time for law firms, which are getting very strong signals from corporate clients that they’re tired of underwriting the latest record profit-per-partner numbers. But the potential impact is greater than that.

I started by suggesting that today’s dominant law firm culture has been shaped by the marketplace realities of the last half-century, which in turn was heavily influenced by demographics. As the Millennials become more and more of a political force within firms, I think you’re going to see a cultural shift too.

Boomers, for whom time was a means to an end, will be replaced by Gen-Yers, for whom time is an end in itself — so how much longer do you think the billable hour system will continue? Boomers think in linear terms and are focused on individual goals, while Millennials collaborate almost by instinct and are natural multitaskers — how long do you think client hoarding will rule and cross-selling will be ignored? Many Boomers still resent e-mail, while Generation Y lives and breathes through online communication — how much longer before extranets, blogs and wikis are part of the everyday fabric of a firm’s operations?

I’m not saying that the march of the Millennials marks the dawn of a golden age — this new generation has plenty of blemishes too, not least an inability to cope with the kind of severe economic downturns that we can expect in short and rapid order. Not all change is good. But it’s reasonable to think that we finally will see law firms break out of their old routines and regimes and start resembling the rest of the 21st-century business world. And there’s actually some irony in that.

Over the years, those of us advocating major operational and cultural evolution in the practice of law have come to despair of effecting change from within. So instead, we’ve been waiting and hoping that clients would throw their weight around and apply sufficient pressure to promote new practices. That’s starting to happen in a few places, but most clients haven’t yet woken up to their own power. It would be fairly ironic, then, if change did end up emanating from inside the profession after all, through the simple manifestation of generational turnover.