African swine fever is an acute haemorrhagic disease of pigs. Extensive recent spread in the Russian Federation and Eastern Europe has increased the risk to global pig production. The virus is a large DNA virus and is the only member of the Asfarviridae family. In pigs the virus replicates predominantly in macrophages. We review how the virus overcomes the barriers to replication in the macrophage and the virus mechanism to inhibit key host defence pathways.