The subject of this monograph is the quaternionic spectral theory based
on the notion of S-spectrum. With the purpose of giving a systematic and
self-contained treatment of this theory that has been developed in the
last decade, the book features topics like the S-functional calculus,
the F-functional calculus, the quaternionic spectral theorem, spectral
integration and spectral operators in the quaternionic setting. These
topics are based on the notion of S-spectrum of a quaternionic linear
operator. Further developments of this theory lead to applications in
fractional diffusion and evolution problems that will be covered in a
separate monograph.