Contextal Advertising
Google's AdSense is perhaps one of the best known contextual advertising programmes.
It works by looking at the page that and advert is to be shown on, and choosing a suitable ad for that page based on the key words shown on the page.
In many cases, this works well: a page about losing weight will have lots of words that attract ads from a weight loss company, for example.
But there are cases when it doesn't work so well: a blog exposing the "myths" of conventional medicine, and suggesting natural remedies for many problems may well target advertisements from mainstream practitioners and companies.
To avoid this, use section targetting.
Section targeing tells Google what sections to take more (and less) notice of when matching ads to page content.
It can be particularly useful to get some parts of sites ignored. For example, if you have a paragraph like
"my site shows blah, blah, blah, excluding foo1, foo2 and foo3"
and foo1, foo2 and foo3 are things that there are a lot of irrelevant ads for, then using targeting to say "ignore the bit starting with excluding" might be a good idea.
For instructions how to do section targeting that works with AdSense, see: https://www.google.com/adsense/support/bin/answer.py?answer=23168
What your readers see
Ideally, the only difference that your readers will see is more relevant advertising.
Related Articles:
Some alternative advertising programmes.
Protect your AdSense ID from malicious use.
Controlling the categories of ads tha tyour blog displays.
