Hi Sally, it really depends which country you come from.
If you are from one of these countries, you do NOT require a visa prior to arriving in Botswana: http://www.botswanaembassy.org/countries-that-do-not-require-visa/ almost 7 years ago
Sally I see you're a US citizen... You are allowed to visit South Africa visa-free for up to 90 days, but you'll need two blank pages in your passport (for affixing stamps and departure stamps) and an onward/return ticket. The same applies to Botswana, so make sure you have enough empty pages.
Phil over 6 years ago