Merge tags (also called personalization tokens or dynamic fields) are placeholders like {{first_name}}, {{company}}, {{city}} that are automatically replaced with each subscriber's actual data at send time. They enable mass personalization without manual editing. Advanced merge tags support conditional logic (show block only if field is not empty) and fallback values ('Hi {{first_name|Friend}}'). MisarMail supports standard merge tags, custom field tags, and AI-generated personalization.