This is a brilliant source book of 20th century design for the home. It covers every period with clear introductions, and then hones in on the key designers for that time.
I love the clarity of the layout. Not only are the pages easy to navigate and 'dip into', the images of the objects are beautifully presented. They stand alone which make them easy to see the detail (and to find things easily when you flick through). The clean images are also a great reference for me (as a designer and illustrator) to redraw the objects.
Other useful and interesting features are timelines at the bottom of the page in each new section to help you see how things developed at a glance (together with imagery of course) and if you're interested in collecting or just curious how much each item is worth, there's estimated values attached to each one.