Due to the technological revolution, in order to withstand competition, giant production companies are obliged to provide customers with the most reliable and safe products in the shortest possible time while keeping the price of the product affordable to customers as well. To achieve this goal, the companies must undertake several complicated tasks, such as making complex dimensional measurements, detecting the defects, and repairing them before bringing the product to market. At that point the non-destructive testing (NDT) comes into play which is a very broad concept containing myriad of conventional and also state-of-the-art methodologies. In this paper, several techniques for NDT, such as X-ray imaging, acoustic emission, ultrasonic testing, infrared thermography, digital image correlation, terahertz testing, shearography will be investigated. Moreover, the principles, advantages and disadvantages and application areas of these techniques will be introduced, and specific examples will be described for some of the methods.