Fog includes a combination of liquid or ice-crystal water droplets suspended in the air, causing a decrease in visibility of less than 1 km in the close by area. Fog formation, dissipation and its occurrence frequency depend on various factors (microphysical properties of cloud condensation nuclei, atmospheric property and boundary layer effect) which can be microscopic, mesoscale and synoptic in nature. Fog occurrences can last for weeks and are responsible for low visibility which directly causes delays, cancellations and tragic accidents of vehicles, trains, flights and ships. The economy has also been affected due to delays and cancellations of transport like rails and flights. This chapter focuses on basic concepts of fog formation, the role of meteorology in fog formation, chemistry of fog, how different chemical constituents present in fog affects its quality and surrounding atmosphere, impacts on plant species, human health, visibility and economy and fog dissipation by cost-effective techniques. It also briefs about different chapters highlighting different features of fog like atmospheric processes, mechanisms, impacts and dissipation strategies.