The Mont Blanc massif is 46 kilometres (29 mi) long and lies in a southwest to northeasterly direction across the borders of France (Haute-Savoie and Savoie), Italy (Aosta Valley) and Switzerland (western Valais).
At its widest point the massif is 20 km (12 mi) across.
The northern side of the massif lies mostly within France, and is bounded by the valley of the Arve, containing the towns of Argentière, Chamonix and Les Houches.
To the west it is bounded by the Val Montjoie, containing Les Contamines-Montjoie and the river Le Bon Nant which flows northwards to a confluence with the Arve near Saint-Gervais-les-Bains, and onwards to the Rhône.

The southern side of the massif lies mostly within Italy and is bounded by the Val Veny and Val Ferret whose watercourses meet just above Courmayeur.
From Courmayeur these waters flow southwards as the Dora Baltea towards Aosta, eventually joining the Po.
However, the extreme western end of the southern side of the massif does lie within France and is bounded by the Vallée des Glaciers (which connects to the Val Veny over the watershed of the col de la Seigne), and its waters flow southwards towards the Isère and onwards to the Rhône.
The northeastern end of the massif falls within Switzerland, and is bounded by a separate valley, confusingly also called Val Ferret, and which separates it from the Pennine Alps further east.
Its watercourse, la Dranse de Ferret, flows northwards to join the Rhône at Martigny.

The borders of all three countries converge at a tripoint near the summit of Mont Dolent at an altitude of 3,820 metres (12,533 ft).
From here the French – Italian border runs southwestwards along a ridge of high summits on the southern side of the massif, many of which are over 4,000 metres (13,123 ft) in height, including the Grandes Jorasses, Rochefort Ridge, Dent du Géant, Mont Maudit, Mont Blanc and its western satellite, the Aiguille de Bionnassay.
From here the border turns southwards over the Dômes de Miage and Aiguille de Tré la Tête before dropping down to the Col de la Seigne.
North of Mont Dolent the border between France and Switzerland meanders roughly north-northwestwards along a ridge-line of slightly lower peaks, including the Aiguille d'Argentière, the Aiguille du Chardonnet and the Aiguille du Tour, before dropping down to the Col de Balme.
The Swiss – Italian border runs southwest from Mont Dolent, down to the twin passes of Col Ferret.

The massif contains 11 main summits over 4,000 metres (13,123 ft) in altitude, as well as numerous subsidiary points above this height.
Crowning the massif is Mont Blanc (4,808 metres (15,774 ft)), the highest mountain in the Alps and in western Europe.
From the summit of Mont Blanc to the Arve near Chamonix there is a 3,800 metres (12,500 ft) drop in altitude over a distance of just 8 kilometres (5.0 mi).
Because of its great elevation, much of the massif is snow- and ice-covered, and has been deeply dissected by glaciers.
The Mer de Glace is the longest glacier in the range as well as the longest in France and the second longest in the Alps.
The debris-covered Miage Glacier on the southern side of the massif is the longest in Italy.

The summit of Mont Blanc is an ice cap whose thickness varies from year to year.

The entire massif can be circumnavigated by the Tour du Mont Blanc, a walking route of approximately 170 kilometres (110 mi).
It usually takes around 11 days to complete, but is also used for an annual mountain ultramarathon, with top competitors expected to complete the whole route in less than 21 hours.

The main mountain passes, or cols, that connect different valleys and towns around the Mont Blanc massif are:
Col du Bonhomme 2,329 m (7,641 ft) (path, links Contamines – Beaufort – Les Chapieux)
Col de la Seigne 2,516 m (8,255 ft) (path, links Bourg Saint Maurice – Les Chapieux – Courmayeur)
Col Ferret 2,490 m (8,169 ft) (path, links Courmayeur – Orsières – Trient valley)
Col de Balme 2,191 m (7,188 ft) (path, links Trient valley – Chamonix)
Col de la Forclaz 1,527 m (5,010 ft) (major road, links Argentière – Martig
The Mont Blanc massif is 46 kilometres (29 mi) long and lies in a southwest to northeasterly direction across the borders of France (Haute-Savoie and Savoie), Italy (Aosta Valley) and Switzerland (western Valais). At its widest point the massif is 20 km (12 mi) across. The northern side of the massif lies mostly within France, and is bounded by the valley of the Arve, containing the towns of Argentière, Chamonix and Les Houches. To the west it is bounded by the Val Montjoie, containing Les Contamines-Montjoie and the river Le Bon Nant which flows northwards to a confluence with the Arve near Saint-Gervais-les-Bains, and onwards to the Rhône.
The southern side of the massif lies mostly within Italy and is bounded by the Val Veny and Val Ferret whose watercourses meet just above Courmayeur. From Courmayeur these waters flow southwards as the Dora Baltea towards Aosta, eventually joining the Po. However, the extreme western end of the southern side of the massif does lie within France and is bounded by the Vallée des Glaciers (which connects to the Val Veny over the watershed of the col de la Seigne), and its waters flow southwards towards the Isère and onwards to the Rhône. The northeastern end of the massif falls within Switzerland, and is bounded by a separate valley, confusingly also called Val Ferret, and which separates it from the Pennine Alps further east. Its watercourse, la Dranse de Ferret, flows northwards to join the Rhône at Martigny.
The borders of all three countries converge at a tripoint near the summit of Mont Dolent at an altitude of 3,820 metres (12,533 ft). From here the French – Italian border runs southwestwards along a ridge of high summits on the southern side of the massif, many of which are over 4,000 metres (13,123 ft) in height, including the Grandes Jorasses, Rochefort Ridge, Dent du Géant, Mont Maudit, Mont Blanc and its western satellite, the Aiguille de Bionnassay. From here the border turns southwards over the Dômes de Miage and Aiguille de Tré la Tête before dropping down to the Col de la Seigne. North of Mont Dolent the border between France and Switzerland meanders roughly north-northwestwards along a ridge-line of slightly lower peaks, including the Aiguille d'Argentière, the Aiguille du Chardonnet and the Aiguille du Tour, before dropping down to the Col de Balme. The Swiss – Italian border runs southwest from Mont Dolent, down to the twin passes of Col Ferret.
The massif contains 11 main summits over 4,000 metres (13,123 ft) in altitude, as well as numerous subsidiary points above this height. Crowning the massif is Mont Blanc (4,808 metres (15,774 ft)), the highest mountain in the Alps and in western Europe. From the summit of Mont Blanc to the Arve near Chamonix there is a 3,800 metres (12,500 ft) drop in altitude over a distance of just 8 kilometres (5.0 mi). Because of its great elevation, much of the massif is snow- and ice-covered, and has been deeply dissected by glaciers. The Mer de Glace is the longest glacier in the range as well as the longest in France and the second longest in the Alps. The debris-covered Miage Glacier on the southern side of the massif is the longest in Italy.
The summit of Mont Blanc is an ice cap whose thickness varies from year to year.
The entire massif can be circumnavigated by the Tour du Mont Blanc, a walking route of approximately 170 kilometres (110 mi). It usually takes around 11 days to complete, but is also used for an annual mountain ultramarathon, with top competitors expected to complete the whole route in less than 21 hours.
The main mountain passes, or cols, that connect different valleys and towns around the Mont Blanc massif are:
Col du Bonhomme 2,329 m (7,641 ft) (path, links Contamines – Beaufort – Les Chapieux)
Col de la Seigne 2,516 m (8,255 ft) (path, links Bourg Saint Maurice – Les Chapieux – Courmayeur)
Col Ferret 2,490 m (8,169 ft) (path, links Courmayeur – Orsières – Trient valley)
Col de Balme 2,191 m (7,188 ft) (path, links Trient valley – Chamonix)
Col de la Forclaz 1,527 m (5,010 ft) (major road, links Argentière – Martig
Mont Blanc massif