Depending on where you meet Brian Kilcourse, you might get a different explanation of how he spends his time.

If you catch him at a work function, for instance, he might introduce himself as a technologist, or president of Retail Systems Research, a consulting firm in Walnut Creek, California. Run into him at a ballgame and he's just as likely to introduce himself as a rock 'n' roll musician.

For Kilcourse, all of these descriptions are accurate. The full-time technology consultant also considers himself a full-time musician, usually spending between 60 and 70 hours feeding both passions each week. Two walls of his office are lined with various computers. The other two are lined with recording equipment and musical instruments.

"I need both to be whole," says Kilcourse, who has recorded multiple CDs. "Sure, there are weeks where I do one more than the other, but when all is said and done, I consider myself equal parts consultant and musician."

Kilcourse is one of a growing number of professionals who see themselves as having multiple careers. According to the U.S. Labor Department, 5.4 percent of the workforce, or 7.9 million people, hold multiple jobs--the highest number since 1999.

Many of these people juggle multiple jobs because they need the money. In special cases, however, people do it to feed passions in two (or more) different areas.

While this double lifestyle is rewarding, it frequently involves long workweeks and blurred lines between personal and professional life. Marci Alboher, who is both a speaker and writing coach, warns that a life of multiplicity may not be right for everyone.

"It can be invigorating and exhausting at the same time," she says. "It's up to everyone with multiple careers to find the balance that works for them."

The "slash" syndrome
Alboher quite literally wrote the book on multiple careers. One Person/Multiple Careers: A New Model for Work/Life Success blazed new trails with the way it chronicled real-life stories from nearly 100 people who successfully transitioned from one career into two.

The book is a paean to passionate souls, profiling people who have followed their hearts toward second careers in professions they love. One man, a personal trainer, moonlights as a narcotics officer for a New York area police department. Another, an actor/director, spends downtime as a landscaper.

Throughout the book, Alboher refers to these people as "slashes," largely because of the way they can use the slash to indicate they take both careers seriously. Under this convention, she describes herself as a speaker/coach/author. She notes that anyone can use a slash to separate any number of careers.

"These people are not ordinary moonlighters or even people with hobbies," says Alboher, who spent years toiling as a lawyer in New York before adding some slashes herself. "They are fully committed to dual or even triple careers."

Dan Milstein demonstrates Alboher's point perfectly. On one hand, Milstein considers himself an independent computer programmer--for the last few years, he's worked for a startup in Waltham, Massachusetts. Yet the 36-year-old also considers himself a thespian, having founded the Rough & Tumble theater in Boston in 1997.

For Milstein, it doesn't matter that 90 percent of his income comes from computer programming, or that the theater gig can sometimes take up 40 hours in a given week. To him, both careers are equally important, elevating each beyond "avocation" status into the realm of something more serious.

"Each profession fulfills me in different ways, and they address very different sides of my brain and personality," he says. "I just don't think I'd be happy doing only one or only the other."

Keeping bases covered
Penelope Trunk knows about the notion of braiding careers, too. In her book, Brazen Careerists: The New Rules for Success, the career columnist for The Boston Globe highlights the importance of interweaving multiple careers to create a tapestry of interests.

For Trunk, family life and personal interests are just as important as professional endeavors and therefore deserve equal consideration during the prioritization process. Here, she says, it's perfectly acceptable for someone to consider the roles of mother, husband, or even uncle as "careers" that deserve equal time.

Another key distinction for her is a push to emphasize both current work and future work, so that every decision you make in the present relates to more long-term goals. "It's an ongoing process," Trunk says. "You need to prepare for that change before it happens, so you're never sitting there wondering what to do next.

Ardyenn Ashley, a self-proclaimed "parallel entrepreneur," certainly has applied this strategy to her world. Today, she considers herself a relationship finance expert, an author, a speaker, and a consultant. Before adding each career, Ashley researched the jobs to the hilt, ensuring that she knew what she was getting herself into.

Her latest move--founding a publishing company--was no exception. After asking other publishers how much time the new job would require, Ashley realized quickly that in order to stay sane, she needed to move her home office out of the house. This summer, she and her husband built a separate office on the property to help separate work and life.

"It gets to a point where what you're talking about is self-preservation," says Ashley, who lives in Petaluma, California, and calls her overarching business Wow Is Me. "If you're working one, two, or three different jobs, you need to know exactly what it's going to take for you to stay on top of everything and still stay sane."

Preserving "me" time
Figuring out this equation isn't easy. The biggest potential problem for multiple careerists is, of course, burnout. Working two careers often means working 60 or 70 hours a week, which can make even the most even-keeled people manic under certain circumstances.

A number of multiple careerists suffer from what Alboher calls "blur," a condition where work bleeds into personal life to such a degree that the two become indistinguishable. One example: a travel writer who is so busy that he forgets to schedule work-free trips (readers, meet your author).

One way to combat this is to establish firm boundaries. Sharon Livingston, president of The Livingston Group, a qualitative research company in Windham, New Hampshire, says that while she works as many as 12 hours a day, she always carves out 30 to 40 minutes for exercise, even if it means simply running up and down her stairs.

"Everybody needs a separation at some point," Livingston says. "If you neglect that separation for too long, you'll burn out, and then where would you be?"

Of course another concern with embracing multiple careers is following your heart into professions that are reasonable. A professional tennis player probably isn't going to have the time to become an award-winning flautist. Similarly, a corporate vice president with a demanding boss may not have the time necessary to become a professional poker player.

Cali Yost, president of Work+Life Fit, a flexibility strategy consulting firm in Madison, New Jersey, says it's important for multiple careerists to remember that excellence in any given area requires 100 percent commitment, and that if you're not willing to give the requisite attention to a second career you may want to think twice about even starting.

"If you want to be an Academy Award-winning actor, I don't know if you can be CEO of a Fortune 500 company, as well," says Yost. "Some of these jobs require a lot of time and energy, so you need to be smart about what you are going to try and achieve."

Matt Villano considers himself a writer, editor, copywriter, whale-lover and husband. He lives in Healdsburg, California.