Human saliva is a complex mixture of various organic and inorganic compounds and host-derived molecules. Performs numerous functions. This comprehensive review will discuss the roles played by saliva in defence against the SARS-CoV-2 virus and the use of saliva as a diagnostic fluid in COVID-19 screening will be discussed along with a brief note on SARS-CoV-2 transmission through saliva. Saliva and SARS Cov 2: The antimicrobial and antiviral properties of saliva are conferred by the salivary peptides such as defensins, cathelicidins, and LL 37. Antiviral activity against the herpes virus, hepatitis C virus, ebola virus and to an extent HIV has been documented. Since the COVID-19 pandemic has now occurred as a new global threat, it is being investigated if saliva has certain properties that could defend against this infection. Studies have found the regular presence of the SARS-CoV-2 virus, the aetiological agent of the COVID-19 disease in saliva, hence saliva could be used as a diagnostic tool. Some interesting findings have highlighted the presence of the virus in salivary samples but documented its absence in throat swabs which is intriguing. Despite having multifaceted roles, the drawback of saliva also lies in its contribution to the transmission of the SARS-CoV-2 virus. Studies have shown that viable viruses can be transmitted through saliva from person to person through coughing and sneezing. Hence saliva could be regarded as a double-edged sword in the COVID-19 pandemic. © 2024 Elsevier B.V., All rights reserved.