The next generation wireless networks will support the vertical handoff procedure in which users can keep the connections when they change from one access network to another. Although diffferent vertical handoff decision algorithms have been proposed in the literature recently. This paper presents an exhaustive state of the art survey about handover alogorithms in heterogeneous networks. With the advent of novel networks technologies, researchers have been working on how to implement and ensure that QoS is achieved in heterogeneous networks. We believe that there have been some improvements, but there is much to do. Additionally, the survey shows the great effort which has been undertaken by the research community in order to address the topic over these years. The blooming of ideas is plethoric and gives us a view about the tremendous scope covered by the subject.