This book contains a systematic and partly axiomatic treatment of the
holomorphic functional calculus for unbounded sectorial operators. The
account is generic so that it can be used to construct and interrelate
holomorphic functional calculi for other types of unbounded operators.
Particularly, an elegant unified approach to holomorphic semigroups is
obtained. The last chapter describes applications to PDE, evolution
equations and approximation theory as well as the connection with
harmonic analysis.