Plants are among the most sensitive organisms to pollutants, often responding with distinct, easy-to-recognize symptoms from exposure to specific environmental contaminants. This characteristic makes plants useful as bioindicators and biomonitors of pollutants. Using plants as bioindicators offers several advantages over physical/chemical monitoring systems: plants are easy to grow and maintain and inexpensive to deploy at a great number of sites; plants integrate pollutant exposure with other environmental factors to provide a biological assessment of exposure; and plant samples may be archived for retrospective analysis. Systems in use include indicator gardens, lichen transplants, plant growth and exposure benches, standard grass cultures, field survey of indigenous or cultivated species, and chemical analysis of plant tissue. A case study illustrating the use of bioindicators to assess the level of fluoride pollution in the Rhône valley in Switzerland is presented.