During the past one decade the Web (currently holding more than 8 billion identifiable and indexed pages) has blossomed from isolated static pages of scientific papers to billion pound revenue dynamic marketing behemoths driven by teams of professional web developers and marketers whose collective duties culminate in a web presence made visible in the search engines. It has revolutionized the way people communicate and deliver information, products and services, not just within a nation but across international borders.

Search Engine Marketing (SEM)-Where SEO deals largely with the mechanical constructs of a web page, Search Engine Marketing (SEM) seeks more to manage and promote a website and its pages across the Internet and, in fact, subsumes SEO within the discipline – albeit as an intrinsic element.
SEM operates at a more strategic level. It defines products and services, examines market strengths and weaknesses, performs competitoranalysis, identifies appropriate web page keywords and phrases, establishes link

(anchor) texts and potential link referrals, looks for directory placements and promotes within the industry. Further, it initiates proactive strategies like PPC (pay-per-click) campaigns like Google’s AdWords or Yahoo’s Search Marketing (formerly Overture) while organic (natural) SEO kicks in.

Websites and pages built using SEO and SEM techniques offer a far higher probability of ranking well in the SERPs and a better return on investment (ROI) than those who have not followed the contemporary techniques. Besides the immediate advantages of strong SERPs, their efficient, to-standards build means greater audience visibility and cheaper maintenance overheads - costs which may not at first seem appreciable but which mount considerably a few months or years down the line.
A few popular web marketing tools:

• E-mail
• Online advertising
• Electronic newsletters
• Loyalty, referral, and affiliate programs
• Web Site

With the "death of banner ads", which used to be the dominant way to pay to get people to visit a web site, and the success of Overture (and now Google AdWords and others), paid placement within search engine results had become very important. Such placement can be within the search listings themselves, or nearby in a special area on the same page. Paying for just showing the listing has in many ways been replace by the more popular paying per click-through, with both fixed and auction-bidding pricing. In addition, there is another thing you can pay for: Pay to be considered for inclusion in the search index. Since some pages aren't found by the search engine spiders, or take a long time to be found, some search engines let a business pay to have the spiders index the content of a page (or an XML version of the contents that they can read).