I'm studying **Bernard Aupetit: A Primer on Spectral Theory**


but the textbook we are using is a little bit heavy going for me. Is there a best book to learn about these things?


Thank you. 



What is the best reference for Spectral theory?
Quite expansive and well detailed are the two books :


* Dunford & Schwartz, *Linear Operators*, Wiley Classics Library, 1971
* Rudin, *Functional Analysis*, McGraw-Hill, 1991


Less specialized but treating very well some parts of the topic is the Brezis, *Functional Analysis* too, and there are many exercises.


Hoping it will be of some use.


