UTM parameters are tags added to URLs that help track where traffic comes from. They're essential for marketing analytics and attribution. Standard UTM parameters: - utm_source: Traffic source (google, instagram, newsletter) - utm_medium: Marketing medium (cpc, email, social) - utm_campaign: Campaign name (summer_sale) - utm_term: Paid keywords (optional) - utm_content: Ad/link variant (optional) Example: yoursite.com/?utm_source=instagram&utm_medium=influencer&utm_campaign=q4_2024 Best practices: - Use consistent naming conventions - Keep values lowercase - Document your taxonomy - Use URL builders for consistency