Conversion Tracking is a form of website traffic analytics that measures the effectiveness of a source directing visitors to a web site and persuading them to take a desired action. The source could be a referrer, a search engine, a search phrase used etc. It could also be a characteristic of the visitor for instance the country, age, income etc. The desired action could be the completion of an order page, the sign-up of a newsletter etc. In affiliate – performance – marketing, conversions are the key metric for the success of an offer. The effectiveness is expressed as a percentage called the Conversion Rate.