Three different principal stresses can be applied in fixed directions to a cubical specimen in this apparatus. The requirements and the construction and operation principles for the cubical triaxial apparatus are presented. The loading system and the deformation measurement principles are described, and procedures for preparing sand and clay specimens are presented. The advantages and limitations of the cubical triaxial apparatus are discussed. The apparatus is relatively inexpensive to build, and it fulfills all basic requirements for high quality soil testing in three dimensions.