In this survey article, we describe recent work that connects three separate objects of interest: totally nonnegative matrices; quantum matrices; and matrix Poisson varieties. on submatrices. The classification is given in terms of certain permutations from the relevant symmetric group with restrictions arising from the Bruhat order.The nonnegative part of the space of real matrices consists of those matrices whose minors are all nonnegative. One can specify a cell decomposition of the set of totally nonnegative matrices by specifying exactly which minors are to be zero/nonzero. In [34], Postnikov classified the nonempty cells by means of a bijection with certain diagrams, known as Le-diagrams. The work of Postnikov was then developed by Talaska [36], Williams [37], etc., and led to the definition of positroid varieties that have been recently studied by Oh [32] and Knutson, Lam and Speyer [23].The interesting observation from the point of view of this work is that in each of the above three sets of results the combinatorial objects that arise turn out to be the same! The definitions of Cauchon diagrams and Le-diagrams are the same, and the restricted permutations arising in the Brown-Goodearl-Yakimov study can be seen to lead to Cauchon/Le diagrams via the notion of pipe dreams.Once one is aware of these connections, this suggests that there should be a connection between torus-invariant prime ideals, torus-orbits of symplectic leaves and totally nonnegative cells. This connection has been investigated in recent papers by Goodearl and the present authors, [14,15]. In particular, we have shown that the Restoration Algorithm, developed by the first author for use in quantum matrices, can also be used in the other two settings to answer questions concerning the torusorbits of symplectic leaves and totally nonnegative cells. The detailed proofs of the results that were obtained in [14,15] are very technical, and our aim in this survey, is to describe the results informally and to compute some examples to illuminate our results.