  In this article we give a brief review of the fundamental physics that can be
done with the future space-based gravitational wave detector LISA. This
includes detection of gravitational wave bursts coming from cosmic strings,
measuring a stochastic gravitational wave background, mapping spacetime around
massive compact objects in galactic nuclei with extreme-mass-ratio inspirals
and testing the predictions of General Relativity for the strong dynamical
fields of inspiralling binaries. We give particular attention to new results
which show the capability of LISA to constrain cosmological parameters using
observations of coalescing massive Black Hole binaries.
