Search Engine Marketing (SEM) is a subtly different subject from the next subject (Search Engine Optimisation, SEO) but it stems from the same premise that most of us use search engines as our first port of call on the Internet (and yes, most of us use Google).
Leaving out SEO, SEM principally covers pay-per-click (PPC), pay-per-acquisition (PPA) and affiliates.
Despite the fact that almost everyone you ask will say they very rarely or never click on a PPC or PPA ad, Google still managed to make the vast majority of its $10.6bn revenue in 2006 out of them.
The challenge for advertisers is to know that PPC / PPA is essentially (or at least should be) a tactical medium. The challenge for digital agencies is to ensure they are geared up to deploy and manage PPC tactically (and therefore often reactively) in order to achieve a solid return on investment for their clients.
Affiliate marketing, meanwhile, is a method of promoting web businesses through advertising on an affiliate (publisher) website, who is then financially rewarded for every visitor, subscriber, customer, and/or sale generated from their site.
Some media agencies target their affiliate placement and some use a more “shotgun” approach. Affiliates are very effective, even a no-brainer, in the right hands.
See also: Online Video Marketing
Search Engine Marketing (SEM): Other Info & Links
Affiliate Marketing - UK Spend 2006