The National Roads and Motorways in Greece constitute the main road network of the country. These two types of roads are distinct in terms of their construction specifications. Their main difference is that motorways (Greek: Αυτοκινητόδρομοι) adhere to higher quality construction standards than National Roads (Greek: Εθνικές Οδοί).

For example, a typical motorway (highway) in Greece consists of six or four lanes (three or two lanes in each direction) plus an emergency lane, separated by a central barrier. Entrances and exits to the motorways are only provided at grade-separated junctions (interchanges) and there are no traffic lights. Greek motorways are generally organized so that the odd-numbered motorways are of north-south alignment and the even-numbered motorways are of east-west alignment. However, there are many exceptions.

A typical National Road in Greece is usually a single carriageway or limited-access road with at-grade intersections and with one or two traffic lanes for each direction, usually with an emergency lane on each side as well. The designation of some important roads of Greece as "national" was first decided by a 1955 decree, while a minister's decision in 1963 determined the numbering of these roads. In 1998, a survey of the Hellenic Statistical Authority defined some new national roads that were constructed after the 1963 decision.

The naming system of motorways and National Roads is different. For example, "A2" refers to the Egnatia Odos motorway, while "GR-2" refers to National Road 2. All motorways are named by using the capital letter "A", followed by a number (e.g. A1). The main motorways of Greece have a single digit number and auxiliary motorways perpendicular to the main ones have a double digit number (e.g. A25). Motorways have their own white-on-green signs, while National Roads are designated by white-on-blue signs.

The construction of the Greek motorway network has been, to a large extent, a very complex and demanding project due to the peculiarities of the geomorphology of the areas through which the new roads pass. The Greek mainland is extremely mountainous; the local topography as well as environmental concerns regarding the local flora and fauna played a decisive role in the final route design. In order to overcome these difficulties, the construction of multiple large and expensive technical works, such as tunnels and bridges, was necessary in many cases. Indicatively, the total number of tunnels built along the four Greek major highways (A1, A2, A5, A8) is about 150 and their total length is about 200 km (measured as a single bore).

With a total length of about 2320 km as of 2020, Greece's motorway network is the biggest one in Southeastern Europe and one of the most advanced in Europe.