Marek's disease (MD) is one of the viral infections that attack poultry and are widespread throughout the world. Vaccination is widely used for the protection of chickens against outbreaks of MD, and commercial vaccines have been used since 1970. There are vaccines derived from three avian herpesvirus serotypes which are propagated in CEF or DEF cell cultures. Most of them are used successfully for vaccination against MDV and are effective and safe. In problem areas where the monovalent vaccine gives poor protection, the use of a bivalent or polyvalent vaccine is recommended for the successful prevention of virulent MDV.