The paper presents two program packages, *FormCalc* and *LoopTools*, for evaluating one-loop amplitudes in four and D dimensions. These programs support both dimensional regularization and constrained differential renormalization (CDR), with CDR being equivalent to dimensional reduction at the one-loop level. The authors discuss the advantages and challenges of each regularization method, particularly in chiral theories and supersymmetric theories. *FormCalc* simplifies symbolic expressions from *FeynArts* and outputs Mathematica expressions that can be further evaluated numerically, while *LoopTools* provides numerical implementations for these expressions. The paper also includes a detailed implementation guide for both programs, an example calculation of the ZZ → ZZ process in the Standard Model, and computer requirements for running the packages.The paper presents two program packages, *FormCalc* and *LoopTools*, for evaluating one-loop amplitudes in four and D dimensions. These programs support both dimensional regularization and constrained differential renormalization (CDR), with CDR being equivalent to dimensional reduction at the one-loop level. The authors discuss the advantages and challenges of each regularization method, particularly in chiral theories and supersymmetric theories. *FormCalc* simplifies symbolic expressions from *FeynArts* and outputs Mathematica expressions that can be further evaluated numerically, while *LoopTools* provides numerical implementations for these expressions. The paper also includes a detailed implementation guide for both programs, an example calculation of the ZZ → ZZ process in the Standard Model, and computer requirements for running the packages.