To visit Bolivia most nationalities only need valid passport (members of EU, Canada and Australia do not need visa - other nationalities please consult with Bolivian consulate in your country – the requirements also change quite often, (citizens of USA, please check with Bolivian Consulate in USA, as of 1st of December 2007, you need visa and it costs U$100, you might be able to get it at the border crossings and airports). The passport must be valid for at least 6 months at the date of entry. If your passport will expire within seven months, we highly recommend that you renew your passport before departing for your trip to Bolivia.
During the entry you will receive a tourist card, this card is free, and you will be given entry stamp which will allow you to stay in the country for 30 days (in some situations it is possible to ask for a longer entry stamp, but there seem to be no fixed rules for this). The tourist card must be returned when you are leaving Bolivia, make sure that you do not loose this card as it might cause problems on exit.
It is advisable that you have two sets of photocopies of all your travel documents, stored at different places (eg. not all in a same piece of luggage). It is also a good idea to scan all your documents and upload them to your email account (eg. Hotmail or Yahoo). That way you will be able to download the images in a case of emergency from any internet café, of which there are large numbers in Bolivia.