  Electron correlations play a central role in iron-based superconductors. In
these systems, multiple Fe $3d$-orbitals are active in the low-energy physics,
and they are not all degenerate. For these reasons, the role of
orbital-selective correlations has been an active topic in the study of the
iron-based systems. In this paper, we survey the recent developments on the
subject. For the normal state, we emphasize the orbital-selective Mott physics
that has been extensively studied, especially in the iron chalcogenides, in the
case of electron filling $n \sim 6$. In addition, the interplay between orbital
selectivity and electronic nematicity is addressed. For the superconducting
state, we summarize the initial ideas for orbital-selective pairing, and
discuss the recent explosive activities along this direction. We close with
some perspectives on several emerging topics. These include the evolution of
the orbital-selective correlations, magnetic and nematic orders and
superconductivity as the electron filling factor is reduced from $6$ to $5$, as
well as the interplay between electron correlations and topological
bandstructure in iron-based superconductors.
