  The HERMES high-resolution spectrograph project aims at exploiting the
specific potential of small but flexible telescopes in observational
astrophysics. The optimised optical design of the spectrograph is based on the
well-proven concept of white-pupil beam folding for high-resolution
spectroscopy. In this contribution we present the complete project, including
the spectrograph design and procurement details, the telescope adaptor and
calibration unit, the detector system, as well as the optimised data-reduction
pipeline. We present a detailed performance analysis to show that the
spectrograph performs as specified both in optical quality and in total
efficiency. With a spectral resolution of 85000 (63000 for the low-resolution
fibre), a spectral coverage from 377 to 900nm in a single exposure and a peak
efficiency of 28%, HERMES proves to be an ideal instrument for building up time
series of high-quality data of variable (stellar) phenomena.

Instrumentation and Methods for Astrophysics