Mosquitoes, often a nuisance during outdoor activities, are also carriers of deadly diseases like malaria, dengue fever, and Zika virus etc. To safeguard against these threats, the use of insect repellents is vital. This chapter explores natural and synthetic repellents, delving into their characteristics, modes of action, and applications. Beginning with a scientific analysis of repellents, it covers the chemical and biological principles behind their effectiveness. Natural repellents derived from plants like citronella and eucalyptus are generally safe but may be less effective. In contrast, synthetic repellents like DEET and picaridin are more potent but may cause skin irritation. The precise mode of action has yet to be fully understood, but repellents are believed to disrupt insects' host-detection abilities. Natural repellents mask the host's odor, while synthetic repellents block insects' olfactory receptors. The chapter concludes with discussions on the ethical aspects of repellent use, DIY natural repellents, and their implications for public health. In summary, it offers a thorough examination of repellents, revealing the science behind their modes of action and their significance in pest control, public health, and ecological sustainability.