'One of its strengths is that it is a genuine textbook rather than a reference text. It is highly readable and pedagogical, giving a good level of detail in proofs, but staying concise and keeping its story clear rather than being encyclopedic. Another strength of the textbook is that it is well motivated by applications of functional analysis to other areas of mathematics, with a special emphasis on partial differential equations and quantum mechanics throughout the book.' Pierre Portal, zbMATH Open
'Everything is beautifully and clearly expressed. In short, highly recommended!' Klaas Landsman, Nieuw Archief voor Wiskunde