In Commutative Algebra certain /-adic filtrations of Noetherian rings,
i.e. the so-called Zariski rings, are at the basis of singularity
theory. Apart from that it is mainly in the context of Homological
Algebra that filtered rings and the associated graded rings are being
studied not in the least because of the importance of double complexes
and their spectral sequences. Where non-commutative algebra is
concerned, applications of the theory of filtrations were mainly
restricted to the study of enveloping algebras of Lie algebras and, more
extensively even, to the study of rings of differential operators. It is
clear that the operation of completion at a filtration has an algebraic
genotype but a topological fenotype and it is exactly the symbiosis of
Algebra and Topology that works so well in the commutative case, e.g.
ideles and adeles in number theory or the theory of local fields,
Puisseux series etc, .... . In Non- commutative algebra the bridge
between Algebra and Analysis is much more narrow and it seems that many
analytic techniques of the non-commutative kind are still to be
developed. Nevertheless there is the magnificent example of the analytic
theory of rings of differential operators and 1J-modules a la
Kashiwara-Shapira.