I will describe ANDES (ArmazoNes high Dispersion Echelle Spectrograph) the optical-infrared High Resolution Spectrograph of the ELT, formerly known as ELT-HIRES, which has started construction activities in 2022 to arrive at the telescope as early as 2031. The project is carried out by an international consortium composed of 33 institutes from 13 countries. The top science cases will be the detection of life signatures from exoplanet atmospheres, tests on the stability of Nature’s fundamental couplings, the direct detection of the cosmic acceleration, the characterization of astrophysical plasmas from the atmospheres of cool stars to the integalactic medium. Many of these science cases require that the instrument is capable of reaching challenging levels of precision and accuracy. I will present an overview of the project, describing science cases and the baseline design. The baseline design, which allows to fulfil the top science cases, consists of a modular fibre-fed cross-dispersed echelle spectrograph providing a simultaneous range of 0.4-1.8 µm with a goal of 0.35-2.4 µm, at a resolution of 100,000 and with several observing modes. The spectrograph will be equipped with both seeing- and diffraction-limited observing modes, the latter being characterised by a unique high resolution IFU, capable of a simultaneous wavelength coverage of 1-1.8 µm. Finally, I will conclude by discussing the challenges in spectral fidelity that ANDES will have to face.