The ever-increasing requirements of product quality and reliability demand more efficient measuring and testing methods that must be online, non-destructive, whole field, and without contact. Developed in the 1990s, shearography - also called speckle pattern shearing interferometry (SPSI) - is a coherent-optical measuring and testing method, similar to holographic interferometry. Unlike holography, however, shearography measures the gradient of the deformation rather than the deformation itself. Consequently, shearography can measure the strain information directly, increasing its importance as an industrial measuring tool. This work describes the development of second-generation digital shearography, which is effective in non-destructive testing (NDT), strain measurement, and vibration analysis due to its relative insensitivity to environmental disturbances.