The dynamics of infectious diseases represents one of the oldest and ri-
est areas of mathematical biology. From the classical work of Hamer
(1906) and Ross (1911) to the spate of more modern developments
associated with Anderson and May, Dietz, Hethcote, Castillo-Chavez and
others, the subject has grown dramatically both in volume and in
importance. Given the pace of development, the subject has become more
and more di?use, and the need to provide a framework for organizing the
diversity of mathematical approaches has become clear. Enzo Capasso, who
has been a major contributor to the mathematical theory, has done that
in the present volume, providing a system for organizing and analyzing a
wide range of models, depending on the str- ture of the interaction
matrix. The ?rst class, the quasi-monotone or positive feedback systems,
can be analyzed e?ectively through the use of comparison theorems, that
is the theory of order-preserving dynamical systems; the s- ond, the
skew-symmetrizable systems, rely on Lyapunov methods. Capasso develops
the general mathematical theory, and considers a broad range of - amples
that can be treated within one or the other framework. In so doing, he
has provided the ?rst steps towards the uni?cation of the subject, and
made an invaluable contribution to the Lecture Notes in Biomathematics.
Simon A. Levin Princeton, January 1993 Author's Preface to Second
Printing In the Preface to the First Printing of this volume I wrote: \
. .