Voltage is 220V, 50 Hz (cycles). One needs to use a transformer (converter) if the appliance one wants to use is 110V. The voltage in the U.S. is 110V, 60 Hz. The wattage of the transformer must match the wattage of the appliance.

The electric plug has two round pins. One needs an adapter plug if one's appliance comes from the US, where two flat pins are used. The adapter plug can be bought at Amazon or at many travel stores.

This website has a very good article about electricity in Europe: