These notes evolved in the process of teaching a beginning graduate course in Hilbert Spaces. The first edition was simply personal, handwritten notes prepared for lecture. A copy was typed and given to the students, for it seemed appropriate that they should have a statement of theorems, examples, and assignments. With each teaching of the course, the notes grew.
A text for the course has always been announced, but purchase of the text has been optional. A text provides additional reading, alternate perspectives, and a source of exercises. Whatever text was used, it was chosen with the intent of the course in mind.