Human metapneumovirus was discovered in 2001. At the same time, it was also revealed that this virus had been circulating in the human population for at least 50 years. In the years that followed, an increasing number of research groups began to publish work on various aspects of HMPV. One of the main concerns was that this virus was detected in a significant proportion of children below the age of 3 years and caused respiratory symptoms very similar to its nearest related human pathogen: human respiratory syncytial virus. Before this study, there had been no large scale study on the prevalence of HMPV in Singapore. There was also no existing data on the presence of HBoV, HCoV and HRV in hospitalized children in Singapore. We screened five hundred clincial nasopharyngeal samples and found that these four respiratory viruses are present in significant proportions. This discovery will hopefully lead to more research interest in the area of respiratory pathogens in children. There is currently no vaccine available against HMPV. Just like other Paramyxoviruses, the fusion and attachment proteins were already known to provide the basis of virus infection. By characterizing the fusion and attachment proteins in HMPV, we confirmed that there was some form of interaction between the two proteins. This information would be useful for initiating further studies which can elucidate the detailed mechanism of this interaction which may lead to the development of antiviral strategies against this pathogen. One of the new advances in vaccine technology involves the use of virus-like particles as immunogens. We successfully produced virus-like particles of HMPV in both mammalian and insect cell lines. Of the two cell lines, the insect cells have the greater potential for mass production of virus-like particles which can be tested as candidate vaccines.