As a society, we produce many types of liquid waste (e.g., municipal sewage, industrial effluent, food processing waste, mine drainage). These waste streams require treatment to reduce their pollutant load (e.g., heavy metals, fecal bacteria and viruses, organic chemicals, biological oxygen demand) prior to being discharged safely into the environment. Plant- and soil-based systems provide a relatively cheap, socially acceptable, effective, and environmentally friendly way of treating a range of wastewaters. This article summarizes the different technologies that can be used to treat different wastewater as well as providing an overview of the major mechanisms involved in pollutant removal.