As viruses spread, small errors - called mutations - arise in the genetic material during replication. Many of these mutations are repaired or die off as the virus continues to move through a population. Mutations that enhance the virus's ability to replicate, transmit, or survive in a host allow the virus to spread more quickly through a population, or become more resistant to immune system defenses, thereby increasing the mutations’ prevalence and creating a new strain of the virus. The purpose of this book is to discuss how variants develop, how researchers identify and sequence variants, and how this information can be utilized by public health officials, government agencies, and medical practitioners to make decisions. The book examines the ways the government can better coordinate its approach to best serve the American people through this pandemic and beyond.