This chapter mainly focuses on the major aspects of the reliability of nondestructive testing (NDT) techniques. From the safety point of view, evaluation of NDT techniques is vital for many risk-involved industries such as in aero-industry, railways, nuclear, oil and gas, etc. In addition, successful implementation of the damage tolerance concept highly relies on the reliability of NDT techniques. In other words, due to the aims of NDE 4.0, the qualitative evaluation of NDT is becoming vital. The first part of this chapter deals with the importance of NDT reliability with regard to the economical, jurisdictional, and safety-critical requirements. Upon highlighting the importance of NDT, the second part of the chapter provides an overview of the understanding on the reliability of NDT. The third and last subsection of this chapter focuses on the topic of the reliability evaluation under NDE 4.0 along with discussion on the need and possibilities of the reliability evaluation.