  A large number of compounds which contain BiS$_{2}$ layers exhibit enhanced
superconductivity upon electron doping. Much interest and research effort has
been focused on BiS$_{2}$-based compounds which provide new opportunities for
exploring the nature of superconductivity. Important to the study of
BiS$_{2}$-based superconductors is the relation between structure and
superconductivity. By modifying either the superconducting BiS$_2$ layers or
the blocking layers in these layered compounds, one can effectively tune the
lattice parameters, local atomic environment, electronic structure, and other
physical properties of these materials. In this article, we will review some of
the recent progress on research of the effects of chemical substitution in
BiS$_{2}$-based compounds, with special attention given to the compounds in the
$Ln$OBiS$_{2}$ ($Ln$ = La-Nd) system. Strategies which are reported to be
essential in optimizing superconductivity of these materials will also be
discussed.
