Most visitors entering Tanzania will require a visa. Visitors can obtain a visa on arrival at either Dar-es-Salaam or Zanzibar airports for US$50, which is payable in cash. All visitors also require some proof of sufficient funds, as well as evidence of their return or onward journey. Passports must have validity of at least six months from the date of entry. Those arriving from an infected country must hold a yellow fever vaccination certificate.
It is advisable to check this information with your relevant embassy prior to travel.
US citizens who do not wish to go through the trouble of dealing with the red tape themselves can count on the professional services of Travel Visa Pro to speed things up: Apply for Tanzania Visa Online (service starts from $39). If you need to renew, add pages, change name, or just get a new US passport, you can Apply for a New US Passport here.