Nice is the major rail crossroads for trains arriving from Paris, other northern cities, and from Italy, too. To reach Nice from Paris (with stops along the coast), you can take the TGV, though it only maintains high speeds to Valence.
You can easily move along the coast between Cannes, Nice, and Ventimiglia on the slick double-decker Côte d'Azur line, a dramatic and tourist-pleasing branch of the SNCF, with more than 40 trains a day. This line is also called the Marseille–Vintimille (Ventimiglia, in Italy). Some of its main stops from Nice are Antibes (30 mins), Cannes (40 mins), and Menton (30 mins); others include Villefranche-sur-Mer, Beaulieu, and Èze-sur-Mer.
For the western parts of the French Riviera, head to St-Raphaël, where the rail route begins its scenic crawl along the coast. There's no rail access to St-Tropez; St-Raphaël is the nearest stop. "Tarifs prem" are the cheapest train fares available from SNCF on a limited number of TGV tickets purchased 90 days before travel date, but there is no exchange. "Loisir" fares are flexible and offer peace of mind for the spontaneous traveler.
SNCF. 3635; www.sncf.com.
TGV. 3635; www.tgv.com.