This chapter describes two of the most adopted software tools for the evaluation of the lightning performance of transmission and distribution lines, namely FLASH and LIOV-EMTP (Lightning Induced OverVoltage - ElectroMagnetic Transient Program), together with some application examples. The FLASH program has been developed by IEEE Working Groups. LIOV-EMTP is the result of the integration between the EMTP and the LIOV code, developed by Alma Mater Studiorum - University of Bologna (Italy), Ecole Polytechnique Federale de Lausanne - EPFL (Switzerland), with the support of University of Rome La Sapienza' and of Centro Elettrotecnico Sperimentale Italiano G. Motta' CESI S.p.A. (Italy).