How Search Engines Work:
The term "search engine" is often used generically to describe both crawler-based search engines and human-powered directories. These two types of search engines gather their listings in radically different ways.>

Crawler-Based Search Engines
Crawler-based search engines, such as Google, create their listings automatically. They "crawl" or "spider" the web, then people search through what they have found. If you change your web pages, crawler-based search engines eventually find these changes, and that can affect how you are listed. Page titles, body copy and other elements all play a role.

Human-Powered Directories
A human-powered directory, such as the Open Directory, depends on humans for its listings. You submit a short description to the directory for your entire site, or editors write one for sites they review. A search looks for matches only in the descriptions submitted.
Changing your web pages has no effect on your listing. Things that are useful for improving a listing with a search engine have nothing to do with improving a listing in a directory. The only exception is that a good site, with good content, might be more likely to get reviewed for free than a poor site.

"Hybrid Search Engines" Or Mixed Results
In the web's early days, it used to be that a search engine either presented crawler-based results or human-powered listings. Today, it extremely common for both types of results to be presented. Usually, a hybrid search engine will favour one type of listings over another. For example, MSN Search is more likely to present human-powered listings from LookSmart. However, it does also present crawler-based results (as provided by Inktomi), especially for more obscure queries.

Buying Your Way In To Search Engines:

When you pay for placement, the process gets speedier, this is why search engine companies like Overture.com (formerly GoTo.com) are growing even in a down economy. "Pay-for-placement search engines usually employ an auction model where the highest displayed ranking goes to the highest bidder. Unlike advertising and other marketing, you typically pay for placement only when it works — about 5 cents per click — so you can quickly decide what's worth the expense.

By nature, search engines are tricky, changeable things, as programmers continually filter spam and work to keep rankings credible and relevant. The time and attention such marketing demands is best handled by automated software or an outsourced provider. But in this tough climate, given the cost and the possible payoff, search engines add up to the best bang you can find for your marketing buck.

Can you buy your way to the top of a search engine? Until 2000, this was almost unthinkable at any search engine other that Overture (formerly GoTo). Now, it's commonplace. Bear in mind that all search engines have some "editorial" style listings that are not bought and sold. Your ad spend will not guarantee a top ranking in these places. However, the space around this editorial copy is considered fair game for ads. So, what's available?

Banner Ads: All major search engines carry keyword-linked banner advertising, either using graphical banners or text banners.

Content Promotion: Many major search engines will promote an advertiser's content, or their own content, on their search results pages. This is usually done in a separate area from the editorial results.

Paid Placement: Several major search engines carry paid placement listings, where sites are guaranteed a high ranking, usually in relation to desired words. The exact position of these listings can vary. Sometimes, they appear above editorial links. Other times, they appear at the bottom of editorial content. "Sidebar" style runs alongside the search engine's editorial area.

Paid Inclusion: This is where an advertiser might be more deeply listed than other sites in the editorial results. Unlike paid placement, this doesn't guarantee a particular position in the main search results. However, also unlike paid placement, it does interact directly with the editorial results. Being more deeply listed can help an advertiser be more likely to appear in response to a wide range of searches.

Paid Submission: This is where a search engine charges to process a request to be included in its listings. Typically, paid submission programs do not guarantee to list a site, only to review and possibly include it in a faster time frame than is normally done. For the purposes of the chart below, paid submission is combined with paid inclusion.