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. An interconnected set of highways can be variously referred to as a "highway system", a "highway network" or a "highway transportation system".

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 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.

World records

• Longest international highway: the Pan-American Highway, which connects many countries in the Americas, is nearly long as of 2005.
• Longest national highway: Australia's Highway 1 at over 20,000 km (12,427 mi). It runs almost the entire way around the country's coastline. With the exception of Canberra (which is inland) it links all the capital cities, although Brisbane and Darwin are not directly connected. Also the route links all the major towns and cities of the island state of Tasmania, Burnie, Devonport, Launceston and Hobart (the state's capital).
• Longest national highway (Point to point): The Trans-Canada Highway (Known as TCH 1 in western Canada) is 7,821 km (4,857 mi) long as of 2006. It runs across southern Canada and connects with several major urban centres along its longitudinal route.
• Largest national highway system: The United States of America has approximately of highway within its borders as of 2005.
• Busiest highway: Highway 401 in Ontario, Canada, has volumes surpassing an average of 500,000 vehicles per day in some sections of Toronto as of 2006.
• Widest highway (maximum number of lanes): The Katy Freeway (part of Interstate 10) in Houston, Texas, United States of America, has a total of 26 lanes in some sections as of 2007. However, they are divided up into general use/frontage roads/HOV lanes, restricting traffic flow.
• Widest highway (number of maximum through lanes): Highway 401 through Mississauga, Ontario has the most unrestricted free-flow lanes, at 18 (22 including restricted) as of 2006.