The Paramyxoviridae family includes many viruses that are pathogenic in humans, 
including parainfluenza viruses, measles virus, respiratory syncytial virus, and 
the emerging zoonotic Henipaviruses. No effective treatments are currently 
available for these viruses, and there is a need for efficient antiviral 
therapies. Paramyxoviruses enter the target cell by binding to a cell surface 
receptor and then fusing the viral envelope with the target cell membrane, 
allowing the release of the viral genome into the cytoplasm. Blockage of these 
crucial steps prevents infection and disease. Binding and fusion are driven by 
two virus-encoded glycoproteins, the receptor-binding protein and the fusion 
protein, that together form the viral "fusion machinery." The development of 
efficient antiviral drugs requires a deeper understanding of the mechanism of 
action of the Paramyxoviridae fusion machinery, which is still controversial. 
Here, we review recent structural and functional data on these proteins and the 
current understanding of the mechanism of the paramyxovirus cell entry process.