This paper discusses two glass-wall techniques-rhizotrons and minirhizotrons. Rhizotrons are covered underground walkways with clear windows on one or both sides. Their design varies somewhat with the type of research to be conducted in them. A minirhizotron consists of a clear tube inserted into the soil then some type of viewing arrangement is lowered into the tube. In both techniques, roots and their rhizosphere organisms can be observed at the soil-wall boundary.