With the invention of high-power computing systems, machines are expected to show intelligence at par with human beings. A machine must be able to analyze and interpret emotions to demonstrate intelligent behavior. Affective computing not only helps computers to improve performance intelligently but also helps in decision-making. This chapter introduces affective computing and related issues that influence emotions. This study also provides an overview of humancomputer interaction (HCI) and the possible use of different modalities for HCI. Further, challenges in affective computing are also discussed, along with the application of affective computing in various areas.