Evangelism marketing is an advanced form of word-of-mouth marketing in which companies develop customers who believe so strongly in a particular product or service that they freely try to convince others to buy and use it. The customers become voluntary advocates, actively spreading the word on behalf of the company.

Evangelism marketing is sometimes confused with affiliate marketing. However, while affiliate programs provide incentives in the form of money or products, evangelist customers spread their recommendations and recruit new customers out of pure belief, not for the receipt of goods or money. Rather, the goal of the customer evangelist is simply to provide benefit to other individuals.

As they act independently, evangelist customers often become key influencers. The fact that evangelists are not paid or associated with any company make their beliefs perceived by others as credible and trustworthy.

Evangelism comes from the three words of 'bringing good news', and the marketing term draws from the religious sense, as consumers are driven by their beliefs in a product or service, which they preach in an attempt to convert others.