NAHUAL is an infrared high-resolution echelle spectrograph for the Great Telescope CANARIAS (GTC) of the Observatorio del Roque de los Muchachos in the island of La Palma. The main scientific objective of the instrument is to measure the radial velocity (RV) with very high precision (goal of 1 m/s) in the near infrared. This will facilitate the detection of exoplanets of low mass (possibly of rocky type) around cool stars and brown dwarfs with spectral types K, M and L (M-type stars are the most numerous in the solar vicinity and in the Milky Way). This can be achieved because of two fundamental reasons: Up to now exoplanets have only been detected with the RV method using optical spectrographs. In the infrared the signal-to-noise ratio (SNR) is increased with respect to the optical for spectral types K, M and L, and hence it is expected to improve the precision in RV measurement rougly linearly with the gain in SNR. When the stellar mass diminishes, the RV amplitude increases for the wobble due to an exoplanet. Therefore, for a given precision in the measurent it is possible to detect exoplanets of smaller mass in the infrared that in the optical. In the infrared the contrast between the photosphere and the magnetic spots that are the cause of the noise in the measurements of RV diminishes. The spots produce asymmetries in the profiles of the spectral lines. Therefore, we expect to increase the sensitivity in the exoplanet detection in young low-mass stars and brown dwarfs using NAHUAL. NAHUAL will also offer to the community a new facility for a great variety of scientific programs, as for example: detailed studies of the atmospheres and cool stars, chemical composition, studies of stellar activity, particularly by means of measurements of magnetic field using the Zeeman effect, characterization of protoplanetary disks, astro-seismology, and characterization of gamma-ray bursts.