Many Internet service companies such as providers of two-sided markets, social networks, or online games rely on the social interaction between their user base and thus capitalize from positive network effects. For such companies, a common strategy is to offer (basic) services for free (and thereby abolish entry barrier of a one-off or recurring price) and to charge their users for premium services. Companies such as eBay, PayPal, LinkedIn, or Skype added paid services to their originally free business models, either via subscriptions, PAYG, or direct sales of virtual items. Their strategy how to make money and whom to bill however differs widely. In the Internet business, ‘monetization’ has become a frequently used buzzword for all aspects of a company’s revenue strategy which includes the decision who should be billed (e.g., for a two-sided market: seller vs. buyer vs. advertisers only), with which price model (e.g., mandatory subscription vs. optional subscriptions vs. selling virtual currency or items) and price level (e.g., differentiated between user groups), and – in case of a freemium strategy – how a new (free) user can be converted most efficiently into a paying and remunerative customer (e.g., via effective CRM measures). The overarching objective of all monetization measures is to maximize the company’s revenue and/or profit. The field of monetization offers a wide field of research opportunities. Four of these are covered in this dissertation: The Name-your-own-price model, users’ spending behavior in virtual communities, the monetization of network effects in social networks, and the legal boundaries of social network usage. As a result, this dissertation solves a series of questions currently being worked on by practitioners and uses a wide range of methods from various disciplines such as economic, psychological, and game theory.