Book excerpt: While many scientists believed influenza would cause the next great pandemic, no one was prepared for the new strain of coronavirus that appeared in 2019. SARS-CoV-2, the virus that causes COVID-19, has infiltrated every country and put global public health and the economy at risk. Health-care systems have been pushed to the limit as protective gear, life-saving equipment, tests, and vaccines are scarce and in high demand. From the initial infection to the widespread impact on daily life, Understanding Coronaviruses examines the intricacies of SARS-CoV-2 and COVID-19 and how they compare to previous viruses and pandemics.