Viruses are obligatory intracellular parasites, constituted of a nucleic acid (DNA or RNA) and a protein capside, while a lipid envelope, which some viruses possess, originated from an infected cell. Viruses do not possess metabolism, hence all steps in their replication cycle depend on host cells which are infected by virus. Viruses are well adapted to host cells and make use of numerous cellular mechanisms, which in cell have roles in metabolic pathways, transport of substances, genome replication or fight against pathogens. This paper describes in detail cell entry strategies of animal viruses. That is the first and often crucial phase in establishing a productive infection. The process itself can be divided into several steps: from initial binding to the cell surface, entry into cytoplasm and transport within the cytoplasm, to the beginning of the replication of the viral genome, either in cell nucleus or cytosol. It is observed that all steps included in cell entry are precisely regulated, and that there is a remarkable diversity of different strategies and adaptations regarding that process, which is presented trough this review.