  In 2012, we discovered superconductivity in Bi4O4S3 and LaO1-xFxBiS2, whose
crystal structures are composed of alternate stacks of a BiS2-type conduction
layer and a blocking layer. Since the discovery, many related superconductors
and functional materials have been synthesized. Furthermore, the possibility of
unconventional superconductivity has been proposed in recent theoretical and
experimental studies. In addition, notable correlations between local structure
and physical properties have been revealed in the BiS2-based systems. In this
review article, we summarize the material development (probably all the
compounds) and physical properties of BiS2-related materials developed in the
last six years. The key parameters for the emergence of bulk superconductivity
in the BiS2-based compounds are carrier doping to the parent phase (band
insulator), pressure-induced structural transition, in-plane chemical pressure,
and the suppression of in-plane disorder. We systematically review those
parameters and the method of designing new superconductors with BiS2 layers. In
addition, studies of BiS2-based compounds as thermoelectric materials are
briefly reviewed.
