Recently, Aaron Karo performed stand-up comedy in a string of sold-out shows. He also bills himself as an author, a public speaker, and a sitcom actor. Karo has always juggled a few careers. After college, he went to work for an investment bank. But he was also writing a weekly newsletter that had tens of thousands of subscribers. And he wrote a book.

About ten years ago, British management guru Charles Handy predicted that people would replace the idea of one, full-time job, with several different part-time occupations. He called this the “portfolio career,” and Karo provides a good example of how this trend is taking shape.

A portfolio career is not the same thing as holding down three bad jobs and wishing you could figure out what to do with yourself. Rather, it is a scheme you pursue purposefully and positively, as a way to achieve financial or personal goals or a mixture of both. This new type of career choice can include several highly skilled, professional posts, often mixing employment with self-employment, and volunteer work or learning work with fee-based work.

While there has been scattered adoption of the portfolio career among baby boomers, the idea is gaining a lot of traction among younger workers, even though they never use the term. The Electronic Recruiting Exchange reports that as many as a third of new workers are looking for alternatives to full-time employment. For people in their twenties and early thirties, a portfolio career is a means of self-discovery, hedging one’s bets, and protecting their quality of life.

Most people have skills that cross into more than one profession. And if you take any one of the popular personality tests offered by web sites and career counselors you will find that peoples’ personalities do not fit neatly into one type of profession either.

So the idea of having to choose one single profession is frequently unappealing. Ezra Zuckerman, associate professor at the MIT Sloan School of Management, told me, “A lot of people feel alienated when thy feel there is more to themselves that they have not shown [in their work].” Young people are particularly drawn to the idea of a career as a vehicle to fulfillment and self-actualization, so they are less apt than Handy’s generation to settle into one, narrow career.

The arguments for a portfolio career at the beginning of one’s adult life are clear. Professor of psychology at Harvard, Daniel Gilbert, told me that the best way to figure out what will make you happy is to try it. A portfolio career gives you the opportunity to try three or four types of work at the same time, and to keep switching out choices until you come up with a portfolio that you like.

Karo, for example, dropped the banking career when he stopped liking the daily suit-and-tie routine. And when I ask him when his next book is coming out, he hems and haws and it’s clear that the career as an author is not so appealing — at least right now.

The trick in all career decisions is to figure out the intersection of your skills and your passions. This is an ongoing process, not a final destination, so a portfolio of part-time careers is more conducive to this path of discovery than a single, eight-hours-every-day career. Andrew Zacharakis, professor at Babson College told me, “Passion is something you have to look for every day of your life. Your passion is likely to change over time but finding your passion is good practice. Part of the search for you passion should be a search to know what your skill set is. Ask parents, mentors, and friends. Try to mach skills you have with your passion.”

The problem with a portfolio career is that you run the risk being a jack-of-all-trades and a master of none — a problem in terms of both money and fulfillment.

“The most secure portfolio careers are with people who have a fairly solid skill base that people will pay for,” says Ian Christie, career coach and author of the Bold Career blog. “You have to hang your hat on something. Either a functional skill, like accounting and you can be, say, a personal trainer at home. Or you need to find a market niche and provide a lot of services, such as training, development, outsource contracting, etcetera.

And you probably need a creative outlet in your portfolio. “When we are involved in creativity we feel that we are living more fully than in the rest of life,” says, Mihaly Csikszentmihalyi, professor of psychology at the University of Chicago. Any work can include creative thinking, but, he told me, “if you want to be creative then you must learn to do something well,” To excel at something requires you to challenge yourself continually. Achieving high skill level at something is an important step toward fulfillment because, “most people want to think they have explored the limits of their potential.”

Karo says he receives a lot of email from people asking how they can follow their creative dreams. And his advice is, appropriately, the Instant-message-length version of Handy’s book-length theory: “You’ve gotta do it on the side. Diversify your revenue streams. Do what you’re passionate about.”