Current vaccines against avian influenza (AI) virus infections are primarily based on classical inactivated whole-virus preparations. Although administration of these vaccines can protect poultry from clinical disease, sterile immunity is not achieved under field conditions, allowing for undetected virus spread and evolution under immune cover. Therefore, there is an urgent need for a robust and reliable system of differentiation between infected and vaccinated animals. Moreover, current AI vaccines must be administered individually, requiring the handling of excessively large numbers of animals, which makes it difficult to obtain high vaccine coverage. Consequently, AI vaccines conferring solid immunity that could be used for mass application would be advantageous. Several approaches are being pursued to improve existing vaccines and develop novel vaccines, all of which will be covered in this overview.