The 96th Tour de France begins on Saturday in Monaco and comprises of 21 stages over 3,500 kilometres.

Cycling's most prestigious event will visit six countries before the finish on the Champs Elysees in Paris on July 26.

The 2009 edition incorporates 10 flat stages, seven mountain stages, one medium mountain stage, two individual time-trials and one team time-trial.

Here we take a look at the stages which could prove decisive.

Stage One, Saturday, July 4, 15.5 kilometres individual time-trial, Monaco

Some surprises can be expected in the prologue around the Principality, which is hosting the Tour for the first time since 1964. The playground of the rich and famous, which borders the Mediterranean, will provide a tough test. The route will touch the fabled Formula One circuit, coming into Casino Square just 1,000 metres in. The route peaks at the Cote de Beausoleil - a 7.2km category four climb - before finishing on the Boulevard Louis II on the seafront.

Stage Seven, Friday, July 10, 224 kilometres from Barcelona to Andorra Arcalis

The 2009 Tour's first venture into the mountains could provide an opportunity for a leading contender to stake a major claim for the yellow jersey. After two category three climbs, a category one climb and a category four climb, the stage culminates with an hors categorie (beyond category) ascent to the finish at the Andorran ski resort of Vallnord. With two further Pyrenean mountain stages to follow in successive days, however, it is likely to prove a day of cat-and-mouse tactics as rivals seek to deplete each other's energy levels.

Stage 15, Sunday, July 19, 207.5 kilometres from Pontarlier to Verbier

One week before the Tour climax in Paris it ventures into the Swiss Alps. With a rest day to follow, some major movement can be expected at the head of the field in the race to Verbier. The most difficult ascent of the day's six climbs is the category one route into the world-famous ski resort, an 8.8km climb at 7.5 per cent.

Stage 20, Saturday, July 25, 167km from Montelimar to Mount Ventoux

For the first time in the race's history, the penultimate stage of the Tour will take place in the mountains. The riders will not see much of the picturesque region of Provence as they grind up Mount Ventoux in a stage which will make the incumbent of the yellow jersey anxious. He will need his team-mates and team car to be vigilant to any breaks and threat to his lead as this is where the 96th edition of the Tour will be decided.