  Classic and recent results for gauge effects on the properties of the
normal-to-superconducting phase transition in bulk and thin film
superconductors are reviewed. Similar problems in the description of other
natural systems (liquid crystals, quantum field theory, early universe) are
also discussed. The relatively strong gauge effects on the fluctuations of the
ordering field at low spatial dimensionality D and, in particular, in thin
(quasi-2D) films are considered in details. A special attention is paid to the
fluctuations of the gauge field. It is shown that the mechanism in which these
gauge fluctuations affect on the order of the phase transition and other phase
transition properties varies with the variation of the spatial dimensionality
D. The problem for the experimental confirmation of the theoretical predictions
about the order of the phase transitions in gauge systems is discussed.
