**Abstract**

Respiratory Syncytial Virus (RSV)-driven bronchiolitis is one of the most common causes of pediatric hospitalization. Every year, we face 33.1 million episodes of RSVdriven lower respiratory tract infection without any available vaccine or cost-effective therapeutics since the discovery of RSV eighty years before. RSV is an enveloped RNA virus belonging to the *pneumoviridae* family of viruses. This chapter aims to elucidate the structure and functions of the RSV genome and proteins and the mechanism of RSV infection in host cells from entry to budding, which will provide current insight into the RSV-host relationship. In addition, this book chapter summarizes the recent research outcomes regarding the structure of RSV and the functions of all viral proteins along with the RSV life cycle and cell-to-cell spread.

**Keywords:** RSV, RNA virus, RNA genome, replicative cycle, fusion protein, cell-to-cell spread, filopodia
