Emerging viruses are viruses that are for the first time identified as agents of diseases in a new host, different geographic area, or both. Re-emerging viruses are are those that have infected humans in the past but continue to appear in different forms. Emerging viruses are a leading cause of emerging viral diseases and can be aetiological agents of epidemics and pandemics. Many factors affect the emergence of a virus and its dissemination, but ecological factors associated with human activities seem to be the most important. Increased contact with wild animals due to the expansion of the human habitat is considered to be the main cause of virus emergence. In the future, emergence of viruses will be more and more common and despite extraordinary technological progress these viruses still remain underexplored. In this paper, four important emerging viruses belonging to two viral families are described: Hendra, Nipah (Paramyxoviridae), West Nile and Zika virus (Flaviviridae). The main aim was to present short overview of their structure, viral cycle, transmission routes, diseases and the ways of their prevention