  Developing realistic and precise models of the electronic properties of
organic molecular crystals is crucial for understanding the full range of
strongly correlated phases that they exhibit. By using \textit{ab initio} model
construction methods, one can obtain unbiased non-interacting models of such
systems from density functional theory, upon which one can base further
(many-body) models. We will discuss the utility and advantages of \textit{ab
initio} model construction using Wannier orbitals. We will briefly review the
approach, and then explain why it is so well suited to molecular crystals in
particular. We discuss the \textit{ab initio} construction of both
non-interacting and interacting Hamitonians, and highlight recent examples
where such first principles models lead to importantly different results than
fitted models.
