Viral marketing and viral advertising refer to marketing techniques that use pre-existing social networks to produce increases in brand awareness, through self-replicating viral processes, analogous to the spread of pathological and computer viruses. It can be word-of-mouth delivered or enhanced by the network effects of the Internet. Viral marketing is a marketing phenomenon that facilitates and encourages people to pass along a marketing message voluntarily. Viral promotions may take the form of funny video clips, interactive Flash games, advergames, images, or even text messages.

It is claimed that a satisfied customer tells an average of three people about a product or service he/she likes, and eleven people about a product or service which he/she did not like. Viral marketing is based on this natural human behaviour.

The goal of marketers interested in creating successful viral marketing programs is to identify individuals with high Social Networking Potential (SNP) and create Viral Messages that appeal to this segment of the population and have a high probability of being passed along.

The term "viral marketing" is also sometimes used pejoratively to refer to stealth marketing campaigns--the use of varied kinds of astroturfing both online and offline to create the impression of spontaneous word of mouth enthusiasm.

• Sending emails with the purpose of acquiring new customers or convincing old customers to buy something immediately.

• Adding advertisements in emails sent by other companies to their customers.

Emails that are being sent on the Internet (Email did and does exist outside the Internet, Network Email, FIDO etc.)

• Compared to other media investments such as direct mail or printed newsletters, it is less expensive.

• An exact Return on investment can be tracked ("track to basket") and has proven to be high when done properly. Email marketing is often reported as second only to search marketing as the most effective online marketing tactic.

• It is instant, as opposed to a mailed advertisement, an email arrives in a few seconds or minutes.

• It lets the advertiser "push" the message to its audience, as opposed to a website that waits for customers to come in.

• It is easy to track. An advertiser can track users via web bugs, bounce messages, un-subscribes, read-receipts, click-throughs, etc. These can be used to measure open rates, positive or negative responses, correlate sales with marketing.

• Advertisers can generate repeat business affordably and automatically

• Advertisers can reach substantial numbers of email subscribers who have opted in (consented) to receive email communications on subjects of interest to them

• Over half of Internet users check or send email on a typical day.

• Specific types of interaction with messages can trigger other messages to be automatically delivered.

• Specific types of interaction with messages can trigger other events such as updating the profile of the recipient to indicate a specific interest category.

• Green - email marketing is paper-free

Permission marketing is a term used in e-marketing. Marketers will ask permission before they send advertisements to prospective customers. It is used by some Internet marketers, email marketers, and telephone marketers. It requires that people first "opt-in", rather than allowing people to "opt-out" only after the advertisements have been sent. The term was coined by Seth Godin in his book of the same name.

Marketers feel that this is a more efficient use of their resources because advertisements are not sent to people that are not interested in the product. This is one technique used by marketers that have a personal marketing orientation. They feel that marketing should be done on a one-to-one basis rather than using broad aggregated concepts like market segment or target market.