**Abstract**

The chapter presented hereafter, outlines the narrow link between chemistry and crystallography that impelled the identification of *polymorphism* and provided a priceless grounding to understand structure-properties relationship. It was initially conceived for organic substances but actually embraced by metal–organic products, especially in the study of coordination polymers. All of the technologic advances have provided profound insights on the control of crystal structures formation revealing that any applied stimulus over a substance can undergo a structural transformation. This has led to the implementation of several methodologies in the industrial and academic segment shedding light on the source of hitherto, not well understood results.

**Keywords:** polymorphism, pseudopolymorphism, solvates, transition metals, organic linkers, crystal structures
