The highway system of the United States is a network of interconnected state, U.S., and Interstate highways. Each of the fifty states, the District of Columbia, Puerto Rico, American Samoa, Guam, and the U.S. Virgin Islands own and maintain their part of this vast system; including U.S. and Interstate highways, which are not owned and maintained at the federal level.

Interstate Highways have the highest speed limits and the highest traffic. Interstates are numbered in a grid: even-numbered routes for east–west routes (but the lowest numbers are along Mexico and the Gulf of Mexico), and odd-numbered routes are north–south routes (with the lowest numbers along the Pacific Ocean). Three-digit Interstates are, generally, either beltways or spurs of their parent Interstates (for example, Interstate H201 is a loop in the city of Honolulu, Hawaii, and is connected to Interstate H1)

U.S. Numbered Highways are the original interstate highways, dating back to 1926. U.S. Highways are also numbered in a grid: even numbered for east–west routes (with the lowest numbers along Canada) and odd numbered for north–south routes (with the lowest numbers along the Atlantic Ocean). Three-digit highways, also known as "child routes," are branches off their main one- or two-digit "parents" (for example, U.S. Route 102 is a branch of U.S. Route 2). However, U.S. Route 101, rather than a "child" of U.S. Route 1, is considered a "mainline" U.S. Highway.

State highways are the next level in the hierarchy. Each state and territory has its own system for numbering highways, some more systematic than others. Each state also has its own design for its highway markers; the number in a circle is the default sign, but many choose a different design somehow connected to their state. Many use an outline of the state with the number inside. Many states also operate a system of county highways.

Over 10,000 articles have been written on Interstate, US, and state roads.