The interest in long-period large-scale oscillations of solar coronal
loops, confidently observed with the modern observational facilities
is mainly connected with the diagnostics of the plasma, known as
the method of magnetohydrodynamic (MHD) seismology. Typical
periods of these oscillations range from a few seconds in flaring
loops to several hours in prominences. Both rapidly decaying and
undamped regimes have been revealed. Observed parameters
of the oscillations give us unique information about the physical
parameters of the plasma, that are either difficult or impossible to
obtain by other methods, such as the magnetic field, fine structuring,
effective transport coefficients and the empirical heating function.
The basic theory used in the interpretation of the observations is
based on the linear MHD perturbations of a straight plasma cylinder,
that predict the existence of three main magnetoacoustic modes:
kink, sausage and longitudinal. Observational manifestation of these
modes in the EUV and microwave bands, and their seismological
implications are discussed. The main emphasis is put on the kink
mode.