This is a technical book and only for those who have a physics degree. Do not think it will be accessable in the same way as a Brief History of Time. What Hawking has done here is to assemble all the original papers on Quantum Theory from the very start to almost the present day. If you are use to reading scientific papers then this will be for you.
The real strength of the book is in the choice of which papers to include and this is where Hawking's expertise comes in. Here you have between the pages of a single volume every important paper that was written by the original discoverers of Quantum Theory; Planck, Einstein, Bohr, Heisenberg, Schrodinger, de Broglie, Feynman, Dirac, Pauli, etc. He includes them all... and even includes the seminal papers of David Bohm from 1952 and John Bells papers on hidden variables which though not considered mainstream are central to undertanding what is behind Quantum Theory. A keyresource book for anyone who wants to study this area seriously and who is not afraid of equations. If you want to really understand Quantum Theory you really need to understand the orginal ideas and thoughts from the people who actually came up with the ideas themselves. This is the only book to do that for you.