Cotrel-Dubousset Instrumentation (CDI) presents a diversified posterior implant system applicable in any situation requiring posterior spinal instrumentation. It acts in the three dimensions of the spine, frontal-sagittal-axial. Correct hook site selection and direction provide spinal balance in three dimensions. The double major idiopathic scoliosis is an appropriate model on which to learn the principles of usage of CDI Results of CDI in a wide variety of spinal pathology have been excellent. There is a learning curve for CDI, hook placement being the most significant. Pitfalls and complications can be avoided.