  Iron-based superconductors are well known for their complex interplay between
structure, magnetism and superconductivity. FeSe offers a particularly
fascinating example. This material has been intensely discussed because of its
extended nematic phase, whose relationship with magnetism is not obvious.
Superconductivity in FeSe is highly tunable, with the superconducting
transition temperature, $T_\mathrm{c}$, ranging from 8 K in bulk single
crystals at ambient pressure to almost 40 K under pressure or in intercalated
systems, and to even higher temperatures in thin films. In this topical review,
we present an overview of nematicity, magnetism and superconductivity, and
discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the
effects of physical pressure and chemical substitutions as tuning parameters.
The experimental results are discussed in the context of the well-studied
iron-pnictide superconductors and interpretations from theoretical approaches
are presented.
