A sportsbook — sometimes called a bookmaker or simply "the book" — is the licensed entity that accepts wagers on sporting events and pays out winning bets. The term "book" traces directly to the physical ledgers that wage brokers historically used to record bets, track payouts, and manage debts. That centuries-old record-keeping practice gave us language we still use every day when we talk about "opening a line" or "moving the number."
How does a legal US sportsbook actually work?
Sports betting involves predicting sports results and placing a wager on the outcome through a licensed sportsbook or bookmaker. When you place a spread bet at a legal US book, you are almost always laying -110 odds — meaning a $110 wager returns $100 in profit — and that built-in margin is how the sportsbook earns its keep on every game. We break down exactly what that cost means for your bankroll in our guide on Vig and Juice in Sports Betting — Why -110 Costs You 2.4%. Legal sportsbooks must also verify your physical location at the moment you place each bet, using geolocation software embedded in the app, so eligibility is determined by where you are standing, not where you live.
What separates a licensed book from an illegal offshore site?
Illegal offshore markets operate entirely outside consumer-protection frameworks, which means there is no regulatory body to contact if a withdrawal is denied, an account is frozen, or odds are manipulated after the fact. State-licensed sportsbooks — operators like DraftKings, FanDuel, BetMGM, and Caesars — are subject to audits, dispute resolution processes, and responsible-gambling requirements mandated by the state that issued their license. The practical difference is recourse: with a licensed book you have it; with an offshore site you generally do not. For a fuller picture of the risks, see our dedicated page on Offshore Sportsbooks — Why Illegal Books Leave Bettors Unprotected.
Which states have legal sportsbooks right now?
As of mid-2025, legal online and retail sports wagering is available in 39 states plus Washington D.C. and Puerto Rico, following the Supreme Court's May 2018 ruling that struck down PASPA. Eleven states have not yet legalized sports betting. Legality — and the minimum betting age, which is 21 in most states though some permit 18+ — varies by jurisdiction and can change quickly, so always confirm current law in your state before depositing. Bonuses and promotional offers from licensed books are also state-specific and subject to terms that operators update frequently.
Where does the word "sportsbook" fit in the wider betting vocabulary?
Understanding what a sportsbook is provides the foundation for everything else in betting terminology — from how lines are set to why certain bet types are offered only at specific books. If you are still building that foundation, our Sports Betting Glossary — Every Picks Term You Need to Know covers the full range of terms in one place. And if you want to understand what analysts mean when they release their recommendations, start with What Are Sports Betting Picks? A Plain-Language Definition before comparing lines across books.
21+ and present in a legal sports betting state to wager. Gambling problem? Call 1-800-GAMBLER.