The U.S. State Department puts it thusly: (France 2014 Crime and Safety Report: Paris) Crime in Paris is similar to that in most large cities. Pickpockets are by far the most significant problem. In addition to purses and wallets, smart phones, and small electronic devices are particular targets. read more
Because there is a risk of theft (as there is anywhere) travelers should consider making use of the hotel safes or at least "hiding" your passport and credit card in your luggage. In the metro/Rer Pickpockets will stand very close to you on the train even if it is not crowded. read more