Visas -- Most travelers can get a 30-day visa on arrival at Bujumbura Airport for $90 USD. A yellow fever vaccination certificate is required. E-visas are also available and worth arranging in advance to avoid potential hassle. Extensions can be applied for in person at the Commissariat General des Migrations in Bujumbura.
Money -- The currency is the Burundi Franc (BIF). Burundi is overwhelmingly a cash economy. ATMs exist at the airport and in Bujumbura but dispense only Burundian francs and are not always reliable. Credit cards are accepted at a handful of upscale hotels and restaurants in Bujumbura and essentially nowhere else. Bring US dollars in good condition -- they are widely accepted for larger transactions and can be exchanged at banks. Do not change money on the street.
Language -- Kirundi is the national language, spoken by everyone. French is the other official language and the language of government and business -- it will get you further than English in most situations. Swahili is spoken along Lake Tanganyika and in Bujumbura. English is understood by some younger, educated Burundians but is not widely spoken. A few phrases of Kirundi or French go a long way.
Safety -- Burundi has improved since the civil war ended in 2005, but it is not a carefree destination. Petty crime is common, particularly in Bujumbura. Political tensions can flare with little warning. The western border areas near Congo are unstable, and the UK government advises against all travel to Cibitoke and Bubanza provinces. Avoid demonstrations, do not travel at night, and keep a low profile. Register with your embassy. Travel with a local guide or reliable contacts if venturing outside Bujumbura.
Health -- Malaria is present throughout the country and prophylaxis is essential. Yellow fever vaccination is required for entry. Medical facilities are extremely limited -- Bujumbura has the best hospitals, but standards are basic by western norms. Carry a well-stocked first aid kit and comprehensive travel insurance with medical evacuation coverage. Drink only bottled or treated water.
Electricity -- 220V, European-style two-pin plugs (Type C and E). Power cuts are frequent, especially outside Bujumbura. A headlamp or torch is essential.
Connectivity -- Mobile coverage is reasonable in Bujumbura and along main roads but patchy in rural areas. Local SIM cards from Econet or Lumitel are cheap and the easiest way to get data. Wi-Fi exists in some hotels in Bujumbura but is slow.