Like all big cities, Paris has its pickpockets.
These few words of advice will help you to avoid any inconvenience: always keep your identity documents and your wallet in sealed pockets, or, for ladies, in a handbag carried across your shoulder.
Try to keep the keys to your accommodation separate from your ID; avoid displaying the contents of your purse, and be particularly vigilant at rush hour when travelling on public transport (9/10am and 6/7.30pm).