  Metal-organic frameworks are a novel family of chemically diverse materials,
which are of interest across engineering, physics, chemistry, biology, and
medicine-based disciplines. Since the development of the field in its current
form more than two decades ago, priority has been placed on the synthesis of
new structures. However, more recently, a clear trend has emerged in shifting
the emphasis from material design to exploring the chemical and physical
properties of those already known. In particular --- while such nanoporous
materials were traditionally seen as rigid crystalline structures --- there is
growing evidence that large-scale flexibility, the presence of defects and
long-range disorder, are not the exception, but rather the norm, in
metal-organic frameworks. Here we offer some perspective into how these
concepts are perhaps inescapably intertwined, highlight recent advances in our
understanding, and discuss how a consideration of the interfaces between them
may lead to enhancements of the materials' functionalities.
