Human immunodeficiency virus (HIV) is a virus that attacks the immune system and causes HIV infection and acquired immunodeficiency syndrome (AIDS). AIDS kills more people than any other infectious disease, and HIV continues to spread faster than any persistent infectious agent known in the last half century. Therefore, it is not surprising that it became one of the most researched infectious particle in the past decade. The important question when it comes to understanding the pathogenesis of HIV infection is not only how the virus causes disease but also why; and these mechanisms are further explained in this paper. Despite its small genome size and its few genes, HIV is extremely successful in taking advantage of cellular pathways while neutralising and hiding from different components of immune system. The most significant advance in the medical management of HIV infection has been the treatment of patients with antiviral drugs, which can suppress HIV replication to undetectable levels and therefore postpone disease progression. Despite the lack of a cure or an effective vaccine, understanding the pathogenesis of HIV infection has yielded important insights that may enable us to design more effective therapeutics for controlling the virus in the future.