This book is one of, if not THE best book I've ever read and has been a massive influence on me.
Laid out in it is a very clear and well argued discussion of how capitalism has freed man from a society that reduced him to a single role, to a position of existential freedom. But at a price. Now man has no fixed position or role, and has to find/create a place for himself in the world. This is a cause of a huge amount of anxiety, and due to man's psychological need to 'belong' to something Fascism, Nazism, nationalism and religious extremism are the result, as they provide a simple "us vs. them" ideology which gives adherent something bigger to be a part of. Also a part of the thesis is how conformity and judgmental (and usually painfully bourgeois) reactionaries are a product of repression, anxiety and just plain resentment.
The psychology takes a lot from Freud, but also moves beyond that - and bettering it in my opinion - avoiding a lot of the pitfalls. It also has a lot of similarity to Camus or Sartre in many ways with a huge emphasis on man's freedom.
This book is of interest to psychologists, philosophers, artists (check out the ending!), and people of all political persuasions.
It's a masterpiece of impassioned humanistic thought, with a real concern (it was written during WW 2) for human freedom, solidarity, creativity and the horrors of Fascism.
Just read it!