  Recent years have brought significant advances in the theory of higher order
elliptic equations in non-smooth domains. Sharp pointwise estimates on
derivatives of polyharmonic functions in arbitrary domains were established,
followed by the higher order Wiener test. Certain boundary value problems for
higher order operators with variable non-smooth coefficients were addressed,
both in divergence form and in composition form, the latter being adapted to
the context of Lipschitz domains. These developments brought new estimates on
the fundamental solutions and the Green function, allowing for the lack of
smoothness of the boundary or of the coefficients of the equation. Building on
our earlier account of history of the subject, this survey presents the current
state of the art, emphasizing the most recent results and emerging open
problems.
