This is a great book to learn Flex, because you get to see a complete application. I used it to connect Flex with Grails instead of Rails. It helps to know a little Flex before you use this book, but it was one of the first books I used to learn Flex, and I am still using it. For example, I used it to see how to handle XML data and error messages sent back from the server. I also used it to learn Cairngorm. I also learned how to send requests via ActionScript instead of MXML. Not part of the book: I am now learning how to connect Flex to Blazeds and Java JPA/Hibernate objects. If this works well, I can use it instead of Grails or Rails on the server side.