This two-hour talk focuses on the estimation of the basic and effective reproduction numbers—key indicators of disease transmissibility—and the assessment of infection risk during a pandemic. Participants will be introduced to the mathematical foundations behind these concepts, including how the reproduction number (R₀ and ​ R_t) reflects the potential for disease spread and guides public health decisions. The session will cover various methods for estimating these values from epidemiological data, with an emphasis on practical approaches such as the use of growth rates and the next-generation matrix. In addition, the talk explores how to quantify the risk of infection in a population, considering factors like contact patterns, susceptibility, and intervention strategies. Real-world examples from recent pandemics, including COVID-19, will be used to illustrate these methods. By the end of the session, participants will have a deeper understanding of how to use reproduction numbers and risk estimates to monitor, predict, and respond to infectious disease outbreaks.