After only two decades from the first detections, we know today about 2,000 planets orbiting stars other than the Sun (exoplanets). Arguably, the ultimate goal of exoplanet science is to find an Earth analog. This task requires us not only to detect planets, but also to accurately determine their properties. Among the observing techniques for investigating the atmospheres of exoplanets, ground-based high-resolution (R>20,000) spectroscopy has recently excelled in delivering robust molecular detections and estimating their relative abundances. The key aspect of this technique is the ability to resolve molecular bands into the individual lines, and to detect their Doppler shift due to the planet orbital motion, complementing traditional measurements of stellar radial velocities. I will review the major breakthroughs achieved in recent years, among which are the first atmospheric detections for non-transiting planets, and the unprecedented measurements of their true masses and orbital inclinations. I will present current efforts focusing on constraining the atmospheric C/O ratio and on measuring the planet rotational rates. Finally, I will review the future prospects of ground-based, high-resolution spectroscopy, including the characterization of Earth-like planets and the identification of possible biomarkers.