  In this review article, we discuss the current status and future prospects of
perturbation theory as a means of studying the equilibrium thermodynamic and
near-equilibrium transport properties of deconfined QCD matter. We begin with a
brief introduction to the general topic, after which we review in some detail
the foundations and modern techniques of the real- and imaginary-time
formalisms of thermal field theory, covering e.g. the different bases used in
the real-time formalism and the resummations required to deal with soft and
collinear contributions. After this, we discuss the current status of
applications of these techniques, including topics such as electromagnetic
rates, transport coefficients, jet quenching, heavy quarks and quarkonia, and
the Equations of State of hot quark-gluon plasma as well as cold and dense
quark matter. Finally, we conclude with our view of the future directions of
the field, i.e. how we anticipate perturbative calculations to contribute to
our collective understanding of strongly interacting matter in the coming
years.
