  Emerging in the 1950s, the multiband superconductivity has been considered
for a long time as an approximate model in the form of a generalization of the
BCS theory to the case of two bands for a more accurate quantitative
description of the properties and characteristics of such superconductors as
cuprates, heavy fermions compounds, metal boron carbides, fullerides, strontium
ruthenate etc. due to their complex piecewise-continuous Fermi surfaces.
However the discovery of the multiband structure of the superconducting state
in magnesium diboride in 2001 and iron oxypnictides and chalcogenides in 2008
led to the appearance of many papers in which effects and different dependences
well known for conventional single-band s-wave superconductors were reexamined.
The main purpose of these studies was to reveal the symmetry type of the order
parameter, which provides an important information about the mechanism of
Cooper pairing in these superconductors. One of the most effective methods of
obtaining information on the symmetry properties of the order parameter in the
multiband superconductors is phase-sensitive techniques. This review summarizes
the results of theoretical and experimental studies of the proximity and
Josephson effects in systems based on multiband superconductors in contact with
normal metals, insulators and other superconductors.
