  Advances in our ability to understand and utilize the world around us have
always relied on the development of advanced tools for probing and manipulating
materials properties. X-ray matter interactions played a critical role in the
development of the modern theory of solid-state materials that has continued
over more than a century. The development of ever-brighter x-ray sources has
facilitated ever more sensitive x-ray scattering and spectroscopy measurements
that are able to probe not just the lattice structure, but also the spectrum of
elementary excitations in complex materials. The interactions underlying the
electronic, magnetic and thermal properties of solids tend to be associated
with lengthscales comparable to the atomic separation and timescales ranging
from femtosecond to picoseconds. The short wavelength, femtosecond pulses from
\gls*{XFEL}s therefore offer unprecedented opportunities to probe and
understand material properties on their natural lengthscales and timescales of
these processes. This chapter reviews a number of exemplary \gls*{XFEL}-based
experiments on lattice and electronic dynamics, and their microscopic
interactions both near and out of equilibrium. We conclude with a brief
discussion of new forms of spectroscopy enabled by the combination of high flux
and short pulse duration and give an outlook for how the field will develop in
the future.
