Restoring posterior teeth is about 80% of our daily practice, and most cavities are of CL II type, so it is all about restoring a healthy and functional proximal anatomy, which means creating correct side profiles and most importantly the height. In fact the proximal ridge is the geode plane for occlusal table with its centric and eccentric movements. So understanding the matrix and the tools that are being used is the key to a successful posterior restoration. This lecture is a summary of all the CL II types and the modern concept for the matrix selection.