Professional networks are by far the most important source of new job opportunities. Networks are critical to your career. But building a powerful network takes time. It takes effort. You must build it before you need it.

Maybe you’re one of the lucky people whose natural charm attracts others. That will get you to first base, but acquaintances don’t make a network. Meeting people won’t be so easy for most of us, but everyone can create a network.

Here are two excellent examples of people who’ve built powerful — but very different — networks. One’s tiny; the other’s enormous. Each was assembled in a very different way.

Industrial CEO Steve (names have been changed) has a network that includes a grand total of three people — two from investment firms, who sometimes need leaders for the industrial companies in their portfolios, and one search firm consultant who serves industrial companies. I was astonished when Steve told me these three people call him about open CEO positions three or four times a year.

Steve’s network’s powerful, even though the only effort he puts into it is the way he handles phone calls. These three people call because they understand Steve and his personal value proposition — narrowly targeting privately held businesses that need to improve manufacturing operations. They know he might be a good candidate for the job they need to fill. Since Steve’s generally content with his current role, he almost always says he’s not interested. But he doesn’t just say, “No thanks,” and hang up. He tries to help the caller. He provides substantive reactions to the job they’re calling about. He suggests others to contact. He calls back if he has an idea later. Doing this doesn’t take long, but it’s helpful, and they appreciate it. So they call again. Talking to Steve is time well spent.

“I take their calls and am helpful. I refer people I know, but I also ask them to refer me. That mutual back-scratching extends my network by quite a bit. I speak to each of them once every two months or so,” he said.

It’s a simple strategic concept. Across his career, Steve learned that productive business relationships result when players help each other. That guides how he structures customer and supplier relationships in his current role. He applied this philosophy to his career. Even though Steve doesn’t aggressively network, by being helpful he’s created a powerful network — the source of his last two jobs.

But few people can depend on just three people. Others put time and effort into building their network. Baxter is the best I’ve found at that.

As a law firm partner, Baxter served electronics and telecoms companies. He became chief legal officer at a telecom client. After several years there, he became general counsel of a startup. A year later, he became CEO of another startup. He moved through similar positions during the dot-com boom. These opportunities came from Baxter’s vast network:

I had literally thousands of contacts. I was known as a fine lawyer with experience in cutting-edge deals and a strong service orientation. Not in a rapacious sense, but I would make it a point to keep up with people. I had a talent at remembering names, what people were interested in, and their faces. I was really good at it. Definitely a competitive advantage. And I made it a point to diligently follow up with notes, birthdays, and so on. I always gave without any expectation of a definite return but also with the belief that what goes around comes around. I’d regularly get calls about job opportunities. Maybe one a week. It was a very “go-go” period.

Baxter worked on building his network almost every week. He kept up with people and referred them to opportunities that might make sense. They enjoyed knowing Baxter and remembered him. They benefited from the acquaintance.

Despite the difference in size and process, Steve and Baxter’s networking strategies have one thing in common: They’re mutually beneficial. Both do more than just meet people; they connect. They pay attention and contribute to what they’re doing. Steve adds insight and ideas. Baxter is memorable, and creates networks not only for himself but for others, too.

Both Steve and Baxter have built their networks over the course of their careers. Their networks bring them surprising opportunities, and they’ll be able to leverage their networks if they ever need a new job.

Finally, both Steve and Baxter are completely genuine. They don’t try to do anything heroic or outside their normal interpersonal styles. It works because they’re comfortable and honest — even when the opportunity presented isn’t right for them. They know what they’re doing is good for everyone involved.

I’ve found few people with networks as strong as either Steve or Baxter’s, but everyone can take lessons from what they did. What has worked for you?