  This is a survey paper based on a series of lectures given at the IHES in
February/March 2015. In a first part, we recall the main results on the
tempered holomorphic solutions of D-modules in the language of indsheaves and,
as an application, the Riemann-Hilbert correspondence for regular holonomic
modules. In a second part, we present the enhanced version of the first part,
treating along the same lines the irregular holonomic case.
