But their passion for locating, identifying and editing information stored on the Internet – soon to be known as “David and Jerry’s Guide to the World Wide Web” – evolved into much more than a hobby, of course.

In March 1995, Yahoo! was incorporated as a business, and by April 1996, our company stock was already being sold publicly on the NASDAQ.

Today, more than 13,000 people from Sunnyvale to Singapore are proud to call themselves Yahoos.

Thank you for celebrating with us all these years–and here’s to many more!

We’ve had the unique opportunity to help create an industry and shape the online world, and will continue to focus on the values that brought us here —working hard, having fun, being passionate about your ideas, believing in each other, and always trying to invent the future.  And as we celebrate 15 years today, we are even more excited than ever about what lies ahead, and the potential of Yahoo! and the Internet.

Of course, we didn’t set out to start one of the world’s largest Internet companies or be leading a movement that has changed the world. We were just a couple of Stanford graduate students doing our research (supposedly) while our professor was on sabbatical.

More interesting than our research was our total fascination with the web and all the cool stuff it suddenly made available. But it was incredibly hard to keep track of the thousands of great websites sprouting up everywhere.  We thought it would be fun to catalog the sites by developing a simple directory. So all this began with nothing more than a hobby to help other early Internet users.

Amazing things happen when we’re doing what’s fun.

We soon learned a huge lesson just as relevant today as then: change and growth on the Internet happen at warp speed—especially if you’re filling a need. With the proliferation of websites and with hundreds of thousands of people accessing our guide, it was simply impossible for us to continue doing this on our own.

Taking big steps takes belief in yourself—and in others.

After many late nights and a lot of pizza, we decided to take the big leap, turn our hobby into a business, raise money and devote ourselves totally to building a company.  This was no sure thing.  For example, 15 years ago, we wanted a free service that was ad-supported. But the conventional wisdom was that our business needed to be subscription-based. Few people thought that advertising could be the key revenue generator for the Internet. Of course, the conventional wisdom was wrong and so today we know that August, 1995, the month our first ad went live, was a critical milestone in the history of Yahoo!, as well as the history of the internet.

Focus on the future: it still looks phenomenal.

Internet growth continues to be simply phenomenal, and we’re nowhere near done.  Fifteen years ago, there were 18,000 web sites and fewer than 10 million people globally on the Internet—less than one third of a single percent of the world’s population at the time. Today there are more than 200 million websites with 90,000 created daily. There are estimated to be 1.6 billion people on the internet today—about 25 percent of the world’s population.

These numbers are astonishing, but even more important and more exciting is the impact that the Internet is having on so many people around the world.  From socio-economic opportunities to more accessible health care to educating the next generation and beyond, the Internet has changed the way we live, work and learn.  It has overcome geographic and political barriers and has made it possible for people to raise their voices as they seek greater economic opportunity and freedom.  And Yahoo! has been a leader in enabling these tremendous technological advancements every step of the way.

Let’s aim to be even prouder fifteen years from now than we are today!

All this in just 15 years. Yahoo! has been built by thousands of dedicated employees, hundreds of millions of loyal users and scores of advertisers who envisioned a future that was exciting, challenging and at times daunting.  To work in the sandbox that is Yahoo! and the evolution of the Internet is truly amazing.

And yet as fast as the Internet and Yahoo! have grown and as remarkably our lives have changed, we are just at the beginning of this great transformation.

The Internet still has enormous and untapped potential.  There are billions of more people we need to drive online, and then provide them with relevant content and opportunities that they’ve never dreamed about before.

We are confident that 15 years from today, we will look back in marvel  at how far you, and the Internet have traveled in such a short time. Just as we are doing today.

Jerry Yang and David Filo

Co-Founders & Chief Yahoos

How the trivia challenge works: We will post each of the 15 questions on our official Yahoo! Twitter account (http://www.twitter.com/yahoo) every hour, starting on March 2nd, 2010 at 8 AM PT. Each question will start with a question number, such as “Q1”, “Q2”, and so on. Find the answer to each question by using the link we provide to the Yahoo! site where the answer can be found. Tweet your response to @yahoo using the hashtag #Y15a. Start your answer with the letter “A” (for “answer”), and the number of the question you’re answering. So, for example, if you’re answering question 5, your reply should look something like:

A5 <this is your answer to Question 5> #y15a.

Easy enough? You can get one entry for each question you answer, for up to 15 possible entries in the challenge. You have until 8 AM on March 5, 2010 to get all of your answers back to us. After the challenge is over, we’ll select the winners from among all the eligible entries we received during the entry period.

What you are playing for: One Grand Prize winner will receive a Nikon Cool Pix S230 Yahoo! Camera and a Jawbone Earcandy Bluetooth Headset (ARV $305). Plus, four first prize winners will each receive a Mimobot Yahoo! USB flash drive. (ARV $20)

Anything else you should know? Our friend Matt the lawyer would also like you know that there’s no purchase necessary and the challenge is void where prohibited. The challenge is open to legal residents of the fifty United States, the District of Columbia, and Canada, excluding the Province of Quebec, who are 18 and older.

Happy hunting!

Start now by following us on Twitter: @Yahoo

For the complete list of rules, click here

Check out more photos here.

Nicki Dugan
Blog Editor

Photo from polvero

What’s that, you say? You don’t know Yahoo! Buzz? It’s where you go to find the Web’s most remarkable stories, determined by people like you. Chances are you’ve read one of the millions of articles that have been “buzzed up,” commented on or featured on the Yahoo! homepage and across Yahoo! sites over the past year. Since Yahoo! Buzz is open to all publishers, the site features stories from tens of thousands of sources –- from the most prolific sites, to the truly quirky.

What we’ve found really interesting is the way people around the Web are busily interacting with the content on Yahoo! Buzz. People are voting on or commenting on stories every two seconds, and the top Yahoo! Buzz stories featured on the Yahoo! homepage to date have received well over 300 million clicks. And while Yahoo! Updates is still relatively new, we’re seeing more and more people sharing Updates from Buzz with their Yahoo! connections. So, whenever you “buzz up” a story, it shows up on Yahoo! Mail, Yahoo! Messenger and other relevant places across Yahoo!, providing another way to share your interests with your connections.

Many thanks to the publishers and the community of people who helped shape the headlines for millions by participating in the first 365 days of Yahoo! Buzz. The site already has more unique monthly visitors than any other social content site in the U.S., according to comScore Media Metrix.

For a look at our editors’ favorite Buzz stories from year one, head on over to the Buzz Log.

We hope you’ll keep on buzzing with us as we watch the next year unfold online.

Brian McMullin
Product Lead, Yahoo! Buzz

Photo from Theresa Thompson