A fun fast paced book that sucks you in right away and doesn't let go. The remnants of humanity live in a 150 story silo below the earth and can't leave as the outside is now toxic. This is a bit of an odd thing to have happened, but it gives us a nice palette to think about things. 
 Everything is rationed, including how many children you can have. People self-identify by their profession and where in the silo they live: farmers and mechanics in the lowers, IT in the mids, and professional class in the uppers. The working class wear color coded uniforms to easily distinguish them. 
 The book was a lot about control. How to control a contained civilization, and give them hope (eg a live feed of the outside) and yet keep them in harmony and doing their functions. Strange mechanisms of control were built all over the silo: communication was oddly limited given the IT resources they have - many messages had to be delivered by courier as emails cost valuable money to send. Most strange of all - there is no elevator, which forces anyone wanting to travel the length of the silo to spend 2-3 days on the journey. 
 The cleaning ritual was a strange bit of culture. Upon reflection, I can see why it was necessary. If people never go outside, uncertainty of it still being bad would creep in, and people would need to try it. As perhaps happened in Silo 17. 
 I really liked the unraveling of Bernard, and how he went from repulsive/annoying, to understandable once you understood his role and responsibility. His role is to eliminate any doubt in the delicate balance of the silo. Opening the book up with the doubt of Holston was brilliant as it sucked you in immediately. 
 I liked Juliet too - she was the right combo of being determined to do right, and having brains and grit.