This publication by the World Health Organization focuses on the integrated sentinel surveillance of influenza and SARS-CoV-2. It examines the development of the Global Influenza Surveillance and Response System (GISRS) Plus, emphasizing the need for effective respiratory virus surveillance. The book highlights the impact of the COVID-19 pandemic on influenza surveillance systems and the progress made in integrating SARS-CoV-2 data. It provides updated guidance on surveillance practices, shares best practices from various countries, and outlines a roadmap for enhancing GISRS towards GISRS Plus. The intended audience includes public health professionals, epidemiologists, and policymakers involved in disease surveillance and response.