In this chapter, we describe an interferometric measurement technique based on the use of laser beams and the Doppler effect, along with its two primary applications for measuring velocity in fluids and on solid surfaces. These two techniques are known as Laser Doppler Anemometry (LDA) and Laser Doppler Vibrometry (LDV). Complementary to LDA, the technique used to measure fluid velocity fields based on image analysis is called Particle Image Velocimetry (PIV). Its measurement principle is similar to that of Digital Image Correlation (DIC), as introduced in Chapter 7. However, PIV employs an optical and experimental setup specifically tailored for fluid flow applications, using tracer particles, light sheet lighting and high-speed imaging to capture and analyze the motion of fluids.