What is UTM parameters?

UTM parameters are tags appended to a URL's query string that identify where a click came from. The three you should always set are utm_source (where: newsletter, twitter, partner-site), utm_medium (how: email, social, cpc), and utm_campaign (why: spring-sale, launch-week). Two optional ones, utm_term and utm_content, add keyword and variant detail. A tagged link looks like example.com/pricing?utm_source=newsletter&utm_medium=email&utm_campaign=launch.

UTMs exist because the referrer header is unreliable: email clients, apps, and privacy features strip it constantly, and untagged clicks collapse into direct traffic. The main pitfall is inconsistency. "Email", "email", and "e-mail" become three sources in your reports, so keep a shared spreadsheet or link builder and agree on lowercase everything. Also never tag internal links on your own site, because doing so overwrites the visitor's real origin mid-session.

Consistent UTMs are the foundation for campaign reporting and any attribution analysis you do later.