This chapter contains sections titled: Introduction Experimental Studies Substrate Binding Substrate Structural Requirements for Catalysis X-ray Structures of Chorismate Mutase Effects of Mutations Activation Parameters Catalytic Mechanism of Chorismate Mutase Stabilization of Transition State by Active Site Residues Substrate Conformational Transition and the Role of Active Site Residues Contribution of the Near Attack Conformers (NACs) Strain Effects and Conformational Compression Conclusion References