I just ordered a copy of this book. So I haven't read it yet. But I did just read this Q&A with the authors (and it clearly piqued interested). The central idea is that Tokyo -- which is a massive city that is famous for somehow being both massive and exceedingly livable -- is the product of something that the authors refer to as emergent urbanism.

What they mean by this is that Tokyo's order, functionality, and livability is actually largely the result of emergent bottom-up actions, rather than top-down central planning. This isn't to say that some top-down planning isn't required for things like parks and transit. You still need some of that. But this is to say that Tokyo's approach to urbanism is very different from what you'll find in cities likes Paris and many others.

Here's an example of what I'm talking about (taken from the above Q&A):

This is going to sound wild to anyone who lives in the US, but for any two-story rowhouse in Tokyo, the owner can by right operate a bar, a restaurant, a boutique, a small workshop on the ground floor — even in the most residential zoned sections of the city. That means you have an incredible supply of potential microspaces. Any elderly homeowner could decide to rent out the bottom floor of their place to some young kid who wants to start a coffee shop, for example. When you look at what we call yokocho alleyways — charming, dingy alleyways that grew out of the black markets post-World War II, which are some of the the most iconic and beloved sections of the city now — it’s all of these tiny little bars and restaurants just crammed into every available space.

What's fascinating about all of this is that we're talking about a kind of self-organizing urbanism. One that goes against everything that traditional city planning stands for. Using the above example, instead of saying that retail should go here, bars should go here, and residences should go only over here, Tokyo is basically saying you can do whatever you'd like.

If you'd like to open a tiny 4-seater bar that only serves Long Island iced teas to people wearing cosplay outfits on neon pink plastic chairs, you are free to do that. Oh, and by the way, we're also going to make it a lot easier and cheaper for you to get a liquor license. This might sound chaotic, but it works for Tokyo. And it's evidence that maybe a lot of our cities would be better off if only we let them be what they want to be.