Since implantable cardioverter-defibrillators (ICDs) were first introduced, defibrillator threshold (DFT) testing was considered an integral part of the implant procedure. Perform‐ ing DFT testing verifies the ability of the ICD in detecting and aborting the lethal arrhythmia it was designed to treat. The process has evolved with the development of the ICD’s and the expanding indications for their usage. Recent studies even questioned the need for DFT as‐ sessment. Currently this matter is controversial with no firm guidelines. In this chapter we present the basic information on DFT testing, how to manage high DFT, and then discuss the evidence for and against performing the test.