Visas. Citizens of most European countries, the US, Canada and many others can enter Tunisia visa-free for up to 90 days (some nationalities up to four months). Check with the Tunisian embassy for your specific nationality before travelling, as the rules change.
Currency. The local currency is the Tunisian Dinar (TND). Dinars cannot legally be purchased outside Tunisia, so bring euros, dollars or sterling and exchange them on arrival. Cash is essential for markets, small restaurants and transport. ATMs are widespread in cities and larger towns. Credit cards work in hotels and smarter restaurants.
Currency controls. Tunisia has strict foreign exchange rules. Keep your exchange receipts -- you'll need them to change dinars back when you leave (you can only reconvert up to 30% of what you exchanged).
Language. Arabic is the official language. French is very widely spoken, especially in business and tourism. English is common in the main tourist areas but much rarer elsewhere. A few words of French will take you a long way.
Safety. Tunisia is one of the safer countries in North Africa for travellers. Petty crime like pickpocketing occurs in medinas and busy areas -- the usual precautions apply. Touts and hustlers operate around major tourist sites; a polite but firm refusal is usually enough. Avoid border areas with Algeria and Libya, and check current advice on any travel to interior areas near Kasserine governorate, which has seen periodic security incidents.
Health. No vaccinations are officially required but hepatitis A and typhoid are recommended. Drink bottled water. The sun in summer is ferocious -- drink more water than you think you need, especially when visiting ruins or walking in the desert.
Religion and dress. Tunisia is a majority Muslim country, and while it is more liberal than many of its neighbours, modest dress is appreciated away from beach resorts and in smaller towns and religious sites. Remove shoes before entering mosques.