  This is a survey paper on derived symplectic geometry, that will appear as a
chapter contribution to the book "New Spaces for Mathematics and Physics",
edited by Mathieu Anel and Gabriel Catren.
  Our goal is to explain how derived stacks can be useful for ordinary
symplectic geometry, with an emphasis on examples coming from classical
topological field theories. More precisely, we use classical Chern-Simons
theory and moduli spaces of flat $G$-bundles and $G$-local systems as leading
examples in our journey.
  We start in the introduction by reviewing various point-of-views on classical
Chern--Simons theory and moduli of flat connections. In the main body of the
Chapter we try to convince the reader how derived symplectic geometry (after
Pantev-To\"en-Vaqui\'e-Vezzosi somehow reconciles all these different
point-of-views.
