Quick: How many entrepreneurs are on the 30 Under 30 list? No, it's not a trick question. The answer is 49. That's because we decided to honor thirty companies this year, many of whom have multiple founders who are age 30 or younger. That's a defining characteristic of this generation of entrepreneurs — they're highly likely to start companies with partners. For them, building a business is not a lone pursuit, but rather an extension of their social lives. In fact, if there's one thing that stands out about this year's coolest young entrepreneurs, it's that their generational fascination with all things social extends deeply into their entrepreneurial zeitgeist.

Simply put, they are growing their companies by building communities.

Now, I know what you're thinking: This is old news, right? Facebook and Twitter taught us all about the power of connecting on the web years ago. And that's true. But the bigger those sites get, the noisier the online world becomes, and the more we long to somehow make our enormous interconnected world a little smaller and a little more manageable again. Like fans that come together at a huge, outdoor concert, we love being with large groups of like-minded people, but we spread blankets to claim our own patch of lawn so that we can gather together the intimate groups of people we care about most.  Likewise, many of our honorees are staking claims in niche areas — on and off the web – where they gather groups of people with the same unmet needs, often connecting customers to one another as well as to their companies.

Take, for instance, Sarah Prevette's Sprouter, a Twitter-like platform that allows entrepreneurs worldwide to connect and collaborate by answering the question "What are you working on?" in 140 characters. The site evolved from Prevette's frustration with her inability to get advice from other business owners when she was starting a previous venture. She longed for a way to connect with other entrepreneurs who were struggling with similar issues or, even better, had found viable solutions to common problems.  Today, Sprouter has more than 15,000 users who share their advice and thoughts on a daily basis. Prevette isn't just the CEO, she's also a happy client, routinely tapping Sprouter's database for advice on additional features and ideas for improvement.

Similarly, when Harvard students Stephanie Kaplan, Windsor Hanger, and Annie Wang created an online version of a campus-based fashion magazine, they attracted so much traffic that they decided to launch a website for college women called Her Campus. Today, the trio cover everything from the latest fashion trends to how to survive a boring internship. The site also houses campus-specific content produced by correspondents at several other colleges and universities, with a total of 42 schools scheduled to be on board by this fall.  For young women, the site breaks down the big world of college life into easy-to-digest chunks.

The list goes on. At Crowdflower in San Francisco, Chris Van Pelt and Luke Biewald assemble a worldwide database of on-demand workers and makes it available to companies that need temporary help on a project-by project basis.

Ooshma Garg's Anapata is a website where minority and female law students connect, network, and upload resumes for perusal by law firms looking to hire a diverse group of associates.

And on AirBnB, hotel-weary travelers can rent an extra room or an entire house from homeowners willing to give up a little space for a little cash. 

Then there's The Man Registry, a website that puts the often-ignored groom front and center by giving him the opportunity to register for gifts such as a turkey frying kit, or an inflatable floating beer pong surface. The site offers purveyors of 'guy goods' a receptive marketplace and gives grooms a way to ask for all the stuff they won't be allowed to buy once they're married.

Community building happens the old fashioned way as well – off line, in the physical world. Tyler Balliet and Morgan First founded The Second Glass to bring wine education and appreciation to their own generation through a series of events call Wine Riot.  You'd be hard-pressed to find a wine snob in the crowd. Attendees, who tend to clamber to the events in groups, can have their pictures taken in goofy costumes, holding up signs that say "I Spit" and "I Swallow." Despite the ribald tone, there's a very real value proposition here: Wine vendors have the opportunity to showcase their best GenY–friendly varietals to a highly engaged and receptive crowd.

Just as The Second Glass promotes wine in a distinctly GenY fashion, so does CityCraft appeal to the next generation of sewers in a way that's decidedly different from your mom's neighborhood fabric center.  Callie Works-Leary's fast-growing Dallas store appeals to young women who seek out not only trendy designer fabrics, but a community in which they can learn, experiment and share ideas. CityCraft has an in-store sewing lounge equipped with cutting tables, machines, and supplies that customers can use on their on own, in one of the store's classes, or during ‘sewing lounge nights' when wine and snacks are serves. For this younger generation of DIYers, even sewing is social.

Also consider Alexa von Tobel, who founded LearnVest, on online resource that teaches twentysomethings about financial management, because she found that existing websites catered mostly to people who were middle-aged and wealthy. LearnVest speaks to a much younger crowd with content on, say, living frugally, shopping for a student loan, and checking your credit score. The Suze-Orman-meets-Mint.com site now has more than 100,000 members.

A close reader by now may have noticed something else about this year's 30 Under 30 roster. We are able to recognize more young women this year, and that makes us very, very happy.  In years past, we've found that it's much been much tougher to find entrepreneurial women under age 30 than it is to find young men.  We're not sure why that is, but this year's search process indicates that we're approaching a tipping point for young female entrepreneurs, and we're thrilled that our list reflects what we hope will be a growing trend.

You'll also notice that while our list contains some incredibly cool web-based companies (Foursquare, Posterous, Milo.com, Songkick, LivingSocial, Venmo, and Crowdflower), we're also featuring a good number of young companies that make products, some of them potentially life-changing. Lauren Bush's FEED Projects makes canvas bags and donates profits to not-for-profit organizations that seek to alleviate hunger worldwide. Sean Whalen's AlterG anti-gravity treadmill will potentially change the rehab process for patients with injuries and debilitating diseases. David Schottenstein's Astor & Black puts a GenY spin on bespoke tailoring. And both Joe McClure's McClure's Pickles and Fraser Doherty's Super Jam have started successful food businesses based on old family recipes.

Lastly, we hope you'll take a good look at our Social Entrepreneurs slideshow, where you'll get a glimpse of the philanthropic causes that our honorees support. That's another characteristic of young entrepreneurs: They tend to integrate social missions into their companies right from the start. Waiting until the big profits start rolling in to infuse their companies with greater meaning just doesn't seem like an option to them. Even as they're getting their businesses off the ground, they are also building time into their schedules to volunteer in places as various as women's shelters and nursing homes, state parks and food pantries, and East Africa and Haiti. In all cases, these business owners are leveraging the core competencies of their companies and their employees to make an impact that goes beyond writing a check.

For a great many of them, it seems, community service is every bit as important as community building—and all of it is wrapped up in an innovative and inspiring entrepreneurial package.