  Multicomponent superconductivity is a novel quantum phenomenon in many
different superconducting materials, such as multiband ones in which different
superconducting gaps open in different Fermi surfaces, films engineered at the
atomic scale to enter the quantum confined regime, multilayers, two-dimensional
electron gases at the oxide interfaces, and complex materials in which
different electronic orbitals or different carriers participate in the
formation of the superconducting condensate. In all these systems the increased
number of degrees of freedom of the multicomponent superconducting
wave-function allows for emergent quantum effects that are otherwise
unattainable in single-component superconductors. In this editorial paper we
introduce the present focus issue, exploring the complex but fascinating
physics of multicomponent superconductivity.
