This chapter describes the role of Color Doppler in infertility. Doppler ultrasonography is a noninvasive procedure that uses detectable changes in high-frequency sound waves (2–20 MHz), based on the Doppler effect, to create clear digital images in real time. Doppler ultrasonography is based on two basic principles following as ultrasound principle and Doppler principle. There are two main types (systems) following as continuous wave system and pulsed wave system. This chapter covers the two-dimensional flow measurement, artefacts, ovary, tubal lesion, uterus, and endometrial and subendometrial blood flow. 2D color Doppler display—uses a computer to convert Doppler measurements into different colors to better visualize the speed and direction of blood flow. Spectral Doppler displays blood flow measurements graphically, in terms of the distance traveled per unit of time, instead of displaying Doppler measurements visually. Duplex Doppler is a type of image display in which both color flow and spectral images are seen at the exact same time.