A friend's recommendation counts more in the purchasing decision than any advertising brochure. How can companies intentionally trigger word-of-mouth? With viral marketing, says Sascha Langner. The idea behind it: information about a product or service spreads from person to person in a very short time, like a virus. Not only Google or GMX are already profitably using such techniques. Even small and medium-sized enterprises can launch successful campaigns with a limited budget. Langner clearly explains what viral marketing entails, what you need to consider when planning and implementing viral actions, and what practical success control looks like. Detailed practical examples, checklists, and additional web links will assist you in designing your own campaign. The 3rd edition has been updated with new insights.