A highway is a main road intended for travel by the public between important destinations, such as cities and towns. Highway designs vary widely and can range from a two-lane road without margins to a multi-lane, grade separated freeway. In law the word highway is often used as a legal term to denote any public road, ranging from freeways to dirt tracks.^[1] An interconnected set of highways can be variously referred to as a "highway system", a "highway network" or a "highway transportation system".^[2]

The United States has the largest network of highways, including both the Interstate highways and United States Numbered Highways. At least one of these networks is present in every state and connects most major cities. The Expressway Network of the People's Republic of China, also known as National Trunk Highway System (NTHS) has a total length of about 53,600 km at the end of 2007, which is the world's second longest system of expressways only after that of the United States.

Some highways, like the Pan-American Highway or the European routes, bridge multiple countries. Australia's Highway 1 is the longest national highway in the world at over 20,000 km (12,000 mi) and runs almost the entire way around the country.

Highways are not always continuous stretches of pavement. For example, some highways are interrupted by bodies of water, and ferry routes may serve as sections of the highway.