It has been nearly ten years since the introduction of SAR by NMR and the advent of fragment-based drug design. During this time, we have gained a tremendous amount of knowledge about protein druggability, the limits of chemical diversity, and crafting high-affinity ligands from low molecular weight, weakly binding leads. This review will describe the concept of fragment-based drug design, discuss why it works, and illustrate the power of the approach with two case studies on the design of potent inhibitors of matrix metalloproteinases and Bcl-2 family proteins.