By now, virtually all small and midsize companies have Web sites. That’s good. The day is coming when virtually all customers will be looking for you on the Web. The question is–will they find you?

Search engine marketing (SEM) is the art and science of making your site visible to on-line searchers. SEM providers work on two fronts–

1. Organic techniques involve building, rebuilding, expanding, or tweaking your site to make it more search engine-friendly. Since the major search engines change what they’re looking for almost daily, SEM techniques evolve rapidly. Optimizing your site for search engines is an ongoing affair, not a one-time shot.

2. Paid search strategies include things like pay per-click (PPC) ads, (There are lots of 3-letter acronyms in marketing. Sorry.) , banner ads, keyword bidding, and email blasts. A big advantage of paid search is its measurability. You can tightly control what you pay and easily calculate your ROI.

In 2005, on-line search surpassed print yellow pages in popularity. We all know that print media is shrinking, figuratively and literally. What may come as a surprise is how rapidly on-line search is growing. Nielsen reports over 5 billion on-line searches were conducted in 2005–a 55% increase from 2004.

Why the surge? Why will it continue?

1. Advances in technology. More users have high speed Internet connections. Wi-fi and Bluetooth, among others, enable users to conduct mobile search. Why thumb through a phone book for a shoe repair shop when you can find one on your PDA?

2. Local search. The most common search term is industry-plus-location. The major search engines–Google, Yahoo!, MSN–all have powerful local search and mapping options that allow users to look for purchases close to home.

3. Demographics. There are a lot of people around who grew up in the digital age. For them, there is no other way to look for products and services. (I think this demographic transition has implications for business that are being seriously neglected–another story.)

SEM should be part of every marketing program. All too often, companies approach SEM haphazardly or not at all. Problems arise when a competitor gets aggressive with SEM, and suddenly, the other guy is building market share at your expense.

For more, ClickZ offers detailed and technical information on technology in marketing.

For an executive view, Lee Odden’s blog is quite helpful.