The Earth is constantly being bombarded with particles from the galactic space and from the Sun with energies that are sufficiently high to penetrate the geomagnetic shielding of the Earth. These high-energy particles, also called primary cosmic rays (CRs), do not reach ground level because they interact with atoms in the atmosphere and initiate air showers producing many secondary particles. Some of these particles, also called secondary CRs, reach the ground and can be detected. An important contribution of secondary CRs to radiation-induced health risks comes from neutrons, because they contribute up to about 60 % to the ambient dose equivalent, H*(10), from CRs at mountain regions. The history of CR measurements can be traced back to the beginning of the 1910’s, when an Austrian-American physicist, Victor Franz Hess, started series of measurements with ionization chambers onboard balloons. Since the 1950’s, neutron monitors are considered as the best ground-based detectors for recording any variations of the primary CR intensity. However, a single neutron monitor does not provide any information on the energy distribution of detected neutrons.This knowledge is important, however, because it can help scientists to understand the nature of CRs. In 1997, major efforts have been made at the Helmholtz Zentrum München (former GSF) when the first ground-based measurement of the energy distribution of neutrons from secondary CRs with an extended-range Bonner sphere spectrometer were performed at the summit of Zugspitze mountain (2,963m a.s.l.), Germany. Since 2005, the neutrons from secondary CRs have been continuously monitored with such a spectrometer at the Environmental Research Station Schneefernerhaus at Zugspitze (2,650 m a.s.l.). The following section of this chapter summarizes general characteristics of CRs, and the three main kinds of shields protecting the Earth from CRs, namely the interplanetary magnetic field, the geomagnetic field, and the Earth’s atmosphere. The next section deals with the definition of effective dose as a protection dose quantity used for the implementation of dose limits. Because effective dose cannot be measured in practice, ambient dose equivalent, H*(10), is described as an operational dose quantity used to quantify external radiation exposures. The third section describes detection principles of the extended-range Bonner sphere spec- trometer installed in an instrument shed at the Environmental Research Station Schneefernerhaus at Zugspitze. All steps necessary for the data evaluation process in terms of detector counts and neutron spectrometry are explained. Special consideration is given to air pressure correction of measured count rates, and to the unfolding process used to derive neutron fluence energy spectra from measured count rates. In the last section, two examples of long-term measurements of neutrons from secondary CRs with one-hour time resolution are shown. First, a rapid decrease within a few hours in measured intensity of secondary CR neutrons, a so-called Forbush decrease, was recognized in the count rates measured in September 2005. Second, the effect of snow cover on the neutron fluence energy spectra at ground level was observed between January 2010 and June 2014.The hypothesis that the snow cover might influence the number of neutrons absorbed or backscattered from soil (so-called albedo neutrons) was tested with Monte Carlo simulations. Finally, seasonal oscillations in neutron fluence due to the presence of a snow cover in winter and its absence in summer are described.