Most people's entire experience of federal tax administration is a letter, and the letter almost never says what it appears to say. This article explains the two separate systems those letters come from — examination, which decides what you owe, and collection, which takes it — and why confusing them is the most consequential mistake a taxpayer can make. It walks through the audit process, the appeal rights that exist at each stage, and the single deadline that determines whether a dispute is heard before or after payment. It then covers collection: liens, levies, the hearings that can stop them, and the settlement options that actually get approved. It closes with penalties, the limitations periods that quietly govern everything, and the practical sequence for handling a notice.