Formalities
Citizens of many countries do not require visas. Check with authorities when planning your trip. You require a valid passport.

Currency
Korean currency is the Korean won (KRW). Few cash machines accept foreign cards, even in Seoul, though there are beginning to be more. Instead bring cash or travelers cheques, which are widely accepted. Exchange services in banks, where administrative procedures are onerous, may take half an hour or more. Payment by bank and credit cards is fairly common. You won't have a problem in large stores or hotels or international restaurants, but they may not be accepted in small neighborhood shops.

Health
No vaccinations are mandatory to enter Korea. The country doesn't present any specific health risks. In generally tap water can be drunk without problem. In any case, have good medical insurance, since the costs of medical care in the country can be quite high.

Electricity
Usually 110 V but 220 V in most hotels. Bring an adaptor.

Clothing
Dress warmly in winter and bring light cottons for the warm, humid summer months. Koreans are very formal, so evening dress is appreciated.

Tipping
Tipping is not customary.

Driving
Renting a car is possible, though hiring a car and driver is preferable if you're not sure of your route, since Korean drivers tend to ignore the rules of the road.

Shopping
In Korea, shopping is a social activity on its own. You should be able to find something to satisfy all your shopping desires: clothing, leather, furs, semi-precious stones, reasonably-priced white jade, medicinal plants… The most interesting destinations are department stores, fairly common in every large Korean city. In Seoul, check out Lotte and Galleria in particular. For antiques, head for the Insa-dong neighborhood. For fashion, go to the Apkujong district. Also check out the bustling business section of Myong-dong, favored by young people, and the immense Namdaemun market. If you like traditional clothing, try to bring back a hanbok, the garment worn by all Korean women, before it is replaced by western fashion.