  The Einstein Telescope (ET) is a proposed next-generation, underground
gravitational-wave (GW) detector to be based in Europe. It will provide about
an order of magnitude sensitivity increase with respect to currently operating
detectors, and furthermore, extend the observation band towards lower
frequencies, i.e., down to about 3Hz. One of the first decisions that needs to
be made is about the future ET site following an in-depth site
characterization. Site evaluation and selection is a complicated process, which
takes into account science, financial, political, and socio-economic criteria.
In this paper, we provide an overview of the site-selection criteria for ET,
provide a formalism to evaluate the direct impact of environmental noise on ET
sensitivity, and outline the necessary elements of a site-characterization
campaign.
