The increase in freshwater contamination due to global population growth, industrialization, emerging anthropogenic pollutants, heavy metals, increased growth of pathogenic microbes and consumption of contaminated drinking water represents a critical problem. Because of these problems, significant emphasis should be placed on the recycling of wastewater. Conventional wastewater management methods require high economic input, provide poor treatment efficiency and cause environmental disbalances by emitting different toxic pollutants. To highlight and alter these types of issues, it is necessary to continuously evaluate the economically feasible technologies and environment-friendly biological methods that complement and improvise the conventional methods. This chapter represents the classifications, sources, characteristics of wastewater, and best-known green technologies available for the treatment of wastewater, as knowing more about the content and sources that discharge the hazardous wastewater may aid in developing more efficient and sustainable wastewater treatment technologies. This chapter also highlighted the different conventional wastewater treatment technologies and different green technologies, including physical, chemical, and biological treatment methods and these methods have been critically reviewed. The state-of-the-art discussed the advantages and limitations of different conventional and modern wastewater treatment techniques. Finally, it overviewed the advantages of the various green technologies used for wastewater treatment and discussed the upcoming, advanced and more promising environment-friendly technologies used for wastewater treatment.