It is this editor's distinct pleasure to offer to the readership the
text of the lectures presented at our recent NATO Advanced Study
Institute held in Cortina d'Ampezzo, Italy between August 6 and August
17, 1984. The invited lectures are printed in their entirety while the
seminar contributions are presented as abstracts. Our Advanced Study
Institutes were originated in 1972 and the reader, familiar with
periodic phenomena, so important in Celestial Mechanics, will easily
establish the fact that this Institute was our fifth one in the series.
We dedicated the Institute to the subject of stability which itself is a
humbling experience since it encompasses all fields of sciences and it
is a basic element of human culture. The many definitions in existence
and their practical applications could easily fill another volume. It is
known in this field that it is easy to deliver lectures or write papers
on stability as long as the definition of stability is carefully
avoided. On the other hand, if one selects a definition, he might be
criticized for using that definition and not another one. In this volume
we carefully defined the specific concept of stability used in every
lecture. If the reader wishes to introduce other definitions we feel
that he should be entirely free and we encourage him to do so. It is
also known that certain sta- bility definitions and concepts are more
applicable to certain given fields than to others.