  The thermal noise is expected to be one of the main limiting factors on the
sensitivity of interferometric gravitational-wave detectors like LIGO and
VIRGO. Thermal fluctuations of internal modes of the interferometer's test
masses and of suspension modes will dominate the noise spectrum at the
important frequency range between 50 and 200 Hz. It is assumed that losses in
the test masses and suspensions will occur mainly due to internal friction in
their materials, which is related to anelasticity effects in solids. The
present notes comprise some basic results on the theory of anelasticity and
thermal noise in pendulum suspensions. This collection is by no means complete
and focus on aspects which are of interest for the author.
