The study of exoplanets is one of the most vibrant fields of astrophysics today. Precise radial velocity (RV, or Doppler) measurements created the field by discovering the first exoplanets. Although employed for more than 30 years, RV measurements are still relevant today; when used with the transit method it provides the first characterization of exoplanets in terms of its mass, radius, and bulk density. These provide the first clues as to the internal structure of the exoplanet. With this text, Hatzes provides a deep understanding of the Doppler method, including how to achieve RV measurement precision, as well as the challenges, limitations, and potential of the technique. It also covers other aspects of the method such instrumentation, wavelength calibration, finding periodic signals in RV time series, signal interpretation, and Keplerian orbits. It's an essential reference for researchers and graduate students in the field of exoplanets, and additionally stellar spectroscopists and instrumentalists.