Natural duality theory is one of the major growth areas within general
algebra. This text provides a short path to the forefront of research in
duality theory. It presents a coherent approach to new results in the
area, as well as exposing open problems.
Unary algebras play a special role throughout the text. Individual unary
algebras are relatively simple and easy to work with. But as a class
they have a rich and complex entanglement with dualisability. This
combination of local simplicity and global complexity ensures that, for
the study of natural duality theory, unary algebras are an excellent
source of examples and counterexamples.
A number of results appear here for the first time. In particular, the
text ends with an appendix that provides a new and definitive approach
to the concept of the rank of a finite algebra and its relationship with
strong dualisability.