Freshwater resources on Earth are limited. They supply water for drinking, irrigation, fisheries, hydropower generation, and many other purposes. Freshwater environments are among the most vulnerable ecosystems. Intensification of agriculture, industrialization, and urbanization coupled with increasing population growth are the main causes of deterioration of freshwater quality. Thus, maintaining the quality of limited freshwater resources on Earth is becoming a global challenge. Reduced water quality disturbs the well-being of human society and the environment in many different ways. Although many countries have identified the importance in maintaining sufficient water quality, actual management efforts at regional or national scale are limited to developed countries because such investments are often costly. As a result, water quality issues in developing countries are poorly attended to. These costs are mainly associated with labor and infrastructure for in- situ water quality monitoring and laboratory analyses because a well-planned management program requires sufficient spatial and temporal coverage. Therefore, cost-effective alternatives for water quality monitoring are on demand. In here, remote sensing of key water quality parameters and estimation of water quality are presently a trending alternative to conventional water quality monitoring practices. Thus, the main focus of this chapter is on justifying the rationale of using remote sensing in water quality assessment with particular emphasis on identifying limitations in conventional water quality monitoring programs and important water quality parameters that are widely used in remote sensing applications and research. This chapter also presents some of the successful remote sensing-based water quality monitoring programs in operation and most widely used satellite sensors onboard and those that are to be launched in future for water quality monitoring. Although remote sensing appears to be a promising alternative, like with any other technological advancements, remote sensing also has limitations in fulfilling objectives of water quality monitoring programs.