The Eifel is bordered by the Mosel River in the south and the Rhine in the east. In the north it is limited by the hills of the High Fens (Hohes Venn), in the west by the Ardennes of Belgium and Luxemburg.
There are several distinct chains within the Eifel.
- The northernmost parts are called Ahrgebirge and rise north of the Ahr River in the district of Ahrweiler.
- South of that river there is the Hohe Eifel ("High Eifel"), with the Hohe Acht (747 m) being the highest mountain of the Eifel.
- In the west, on the Belgian border, the hills are known as Schneifel (originally Schnee-Eifel, = "Snowy Eifel"), rising up to 698 m. Also in the west, by the Belgian and Luxembourg border, the region is known as Islek (Aquilania).
- The southern half of the Eifel is less high. It is cut by several rivers running north-south towards the Mosel. The largest of these rivers is the Kyll, and the hills on either side of this river are called the Kyllwald.
- In the south the Eifel is concluded by the Voreifel above the Mosel.
The Eifel and its western continuation into Belgium, the Ardennes, are a part of the Variscan mountain belt and belong to the Rheinisches Schiefergebirge.
The Eifel consists mainly of Devonian slates, sandstones and limestones, laid down in an ocean south of the Old Red Continent and folded and overthrust in the Variscan orogeny. The Eifel geological structures like main folds and overthrusts can be traced in a SW-NE-dircection far beyond the Rhine valley.
In the Tertiary and Quaternary geological era, the Eifel was a site of extensive volcanic activity. Some of the hills are volcanic vents. The peculiar circle-shaped lakes (maar) of the volcanic regions formed in volcanic craters. The last volcanic eruptions in the Laacher See volcanic site took place around 10 000 years ago and generated a huge volume of volcanic ash, now found in thin ash layers in contemporaneous sediments throughout Europe. The volcanism of the Eifel is thought to be partly caused by a hotspot or mantle plume, a place where hot material from deep in the mantle rises to the surface, and partly by melt-ascent at deep fractures in the earth's crust. Research has shown that the volcanism is still active; the Eifel region is rising by 1-2 mm per year. Historically, the Eifel volcanoes had inactive phases of 10,000 to 20,000 years between active phases, suggesting there is a possibility of future eruptions.
- Since 2004 about 110 km² of the Eifel have been protected as the nature reserve Eifel National Park.
- The Nürburg Ring, one of the world's most famous motor racing courses, is located in the Eifel. The northern loop (Nordschleife) of the course is also known as the Green Hell (Grüne Hölle), because of its long, difficult and dangerous path through the local forest.
- An interesting archeological feature of the region is the Eifel Aqueduct, one of the longest aqueducts of the Roman empire, providing the city of Cologne with water.
- The Eifeler Regel in Luxembourgish orthography