While each country has its own currency, dollars either will work there, or are easily exchanged.  Most cities, towns, and airports have ATM machines, which offer excellent exchange rates.  The very good news is that the exchange rate is very favorable at the moment, and makes food and wine an unbelievable bargain right now.  Visa or Master cards work at most major lodges, hotels, or restaurants.  Note all credit cards are't created equal.  Try to use ones that don't charge an International transaction fee. Before you depart, notify your credit card company of the countries you will be visiting and the dates you will be there, so you won't experience any credit denials. 

South Africa deals in Rands, most other countries price in US dollars go to for current Rand conversions, but remember commissions are involved, so you never get exact exchange rates, but it is a good reference.

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