The first and second countries that I’ll be visiting during my upcoming trip to Africa will be Kenya and Tanzania where as a U.S. citizen, not only will I need a passport that will be valid for 6 months with blank pages, as well as a yellow fever vaccine, I will also need tourist visas in order to enter both.
Kenyan Immigration has a strict visa policy, and encourages visitors to use their online system to obtain one (though at this exact time all Kenya government websites are down). Only for a short while longer will single-entry visas be available upon arrival at Kenya’s ports of entry such as the Jomo Kenyatta International Airport in Nairobi. It is important that your passport is valid for at least six months from the end of the trip, as some airlines may not even let you board as in the linked Reddit post, and has two blank pages. You will also need proof of Yellow Fever immunization, typically in the form of an international certificate filled out when you get the vaccination, with the immunization being good for 10 years.
Tanzania also requires visas for U.S. citizens, which can be obtained before travel, but are also available at ports of entry upon arrival. As with Kenya, and most other countries really, Tanzania requires a passport that is valid for a minimum of six months and one blank page. You will also need to present a round-trip ticket and demonstrate that you have sufficient funds for your stay. Proof of yellow fever immunization is also required if arriving from or transiting through yellow fever endemic countries, with Kenya as one example. The Embassy of Tanzania for the U.S. has an information page on obtaining a visa, and is linked below. Signing up for a visa requires providing your actual passport, two recent passport size photos, your flight itinerary, a completed application form, a return envelope, and a fee of $100 for U.S. citizens. Regular processing takes five business days, and can be expedited to 3 days or 1 day by paying additional fees. This process can ultimately take about one to two weeks plus mailing time.
References:
Department of State, Travel: Kenya