  Transition metal ions play crucial roles in the structure and function of
numerous proteins, contributing to essential biological processes such as
catalysis, electron transfer, and oxygen binding. However, accurately modeling
the electronic structure and properties of metalloproteins poses significant
challenges due to the complex nature of their electronic configurations and
strong correlation effects. Multiconfigurational quantum chemistry methods are,
in principle, the most appropriate tools for addressing these challenges,
offering the capability to capture the inherent multi-reference character and
strong electron correlation present in bio-inorganic systems. Yet their
computational cost has long hindered wider adoption, making methods such as
Density Functional Theory (DFT) the method of choice. However, advancements
over the past decade have substantially alleviated this limitation, rendering
multiconfigurational quantum chemistry methods more accessible and applicable
to a wider range of bio-inorganic systems. In this perspective, we discuss some
of these developments and how they have already been used to answer some of the
most important questions in bio-inorganic chemistry. We also comment on ongoing
developments in the field and how the future of the field may evolve.
