A sportsbook is a gambling establishment that accepts bets on sporting events and pays winning bettors. It also offers odds on these bets, which are determined by the probability that something will happen.

The American Gaming Association estimates that 18% of American adults placed a wager on sports last year, with most of that money being wagered at legal venues. That represents a remarkable change for an industry that was nearly entirely illegal just two years ago.

Sportsbooks are an integral part of many online gaming brands and often accompany a full racebook, casino and live dealer table games. These services can be very profitable, especially in the US where betting is legal in Nevada and several other states. Nevertheless, operating a sportsbook requires careful planning and an understanding of regulatory requirements and market trends.

The best online sportsbooks provide large menus of sports, leagues and events as well as a variety of different bet types. They also offer fair and reasonable odds as well as secure privacy protection for their customers. Additionally, many of these sites are established and trusted brands with a long track record in the iGaming industry.

In Las Vegas, the majority of Sportsbooks are associated with casinos and prefer to take action from hotel guests and recreational gamblers. This has led some books to reduce their betting limits and even refuse action from professional bettors. However, the growth of eSports and the pandemic have prompted some Sportsbooks to offer broader betting markets and rethink their limits.