The world of Indoor Air Quality has gone through a major transition since January of 2020. Researchers and practitioners, including those in the air filtration industry, are in high demand to provide good information on how to deal with the spread of Covid-19. Building owners and managers need answers to the many questions about making their facilities safer so that they can be used productively. This presentation will focus on how air filters affect indoor air quality and how air filters can be used to limit exposure to Covid-19 aerosols. It will cover filter efficiency and explain why certain levels of filtration are being recommended. But it will also focus on filter “effectiveness” and draw on recent research to cover how and where filters should be used to obtain optimum results.