The emergence of SARS-CoV-2 (the virus responsible for COVID-19) has shifted our approaches to research and public health on infectious diseases. Globally, scientists have been struggling with the biology, behaviour, and consequences of the virus since its emergence in late 2019. This chapter provides an overview of the virus which is human-centered; explaining the intricate processes of how the virus enters our body, replicates, mutates, and interacts with the immune system. Gaining insight into the core science of SARS-CoV-2 will shed light on the virus's infectiousness, how diagnostic tools and treatment protocols are developed. This chapter attempts to help medical researchers and health professionals understand the intricate details of COVID-19 epidemiology.