CPL – Cost per lead. This is the most popular way to buy media. CPL means that the advertiser pays when a lead form is completed and submitted. This solution is very common in B2B marketing, where it is less likely that someone makes a purchase immediately. There are two popular variants of this solution. We have SOI – single opt-in, that doesn’t require the user to verify his or her email address, and DOI – double opt-in which means that user has to verify his or her email address. CPL is limited to collecting leads forms. It is used in lead generation campaigns, so the ultimate goal is to get data like e-mail addresses from potential customers.This model is perfect for promoting wide range of products.