The results of recent research on joint design and joint sealants are now becoming available to the architect, engineer and contractor, which together with a whole new line of sealants of the two-component type, have brought a radical change in the thinking in the design of joints and in the practical installation of them. Since joints must be designed to prevent joint failure, the causes of joint failure must first be investigated. Studies have revealed that the three basic causes behind joint failures are: (1) poor joint design, mainly due to the failure of the designer to calculate and allow for the movement in the joint. (2) The use of the wrong type of sealant for the service conditions to which the joint will be subjected. (3) Poor workmanship in preparing the surfaces and in mixing and applying the sealant selected. The key then to proper joint design is the proper spacing of the joints, their size and the shape factor which the sealant will take after being applied in the joint. These elements, in conjunction with the type of sealant selected, will make the difference between a successful and an unsuccessful joint sealing project.