  In this presentation we shall deal with some aspects of the theory of Hilbert
functions of modules over local rings, and we intend to guide the reader along
one of the possible routes through the last three decades of progress in this
area of dynamic mathematical activity. Motivated by the ever increasing
interest in this field, our goal is to gather together many new developments of
this theory into one place, and to present them using a unifying approach which
gives self-contained and easier proofs. In this text we shall discuss many
results by different authors, following essentially the direction typified by
the pioneering work of J. Sally. Our personal view of the subject is most
visibly expressed by the presentation of Chapters 1 and 2 in which we discuss
the use of the superficial elements and related devices. Basic techniques will
be stressed with the aim of reproving recent results by using a more elementary
approach. Over the past few years several papers have appeared which extend
classical results on the theory of Hilbert functions to the case of filtered
modules. The extension of the theory to the case of general filtrations on a
module has one more important motivation. Namely, we have interesting
applications to the study of graded algebras which are not associated to a
filtration, in particular the Fiber cone and the Sally-module. We show here
that each of these algebras fits into certain short exact sequences, together
with algebras associated to filtrations. Hence one can study the Hilbert
function and the depth of these algebras with the aid of the know-how we got in
the case of a filtration.
