Digital shearography : new developments and applications Since the second industrial revolution the industry is always seeking for more efficient measuring and test methods in the aim of reaching higher production quality and reliability. With the invention of the first functioning laser in 1960 a modern evolution of optical measurement methods begins. Laser based modern optical measurement methods take the advantages of extremely high sensitive and noncontact which make them as ideal ways for nondestructive online and whole field test in industry applications. Shearography also called speckle pattern shearing interferometry is a laser speckle pattern interferometry based measurement technique. It measures the gradient of the deformation. In order to provide a better understanding of the digital shearography technique this chapter gives a brief review of basic optics principles by reviewing the properties of laser wave equations and speckle pattern phenomenon