Jacobs, who died last month, believed that the planners who gave us the housing project, the suburb, and hideous "urban renewal" projects like the World Trade Center and Lincoln Center, were using ideals and theories developed by people who actively hated cities, rather than paying attention to how real cities worked. "This is not the rebuilding of cities," she says in the introduction. "This is the sacking of cities." Forty years ago she pointed out the glaringly obvious truth that this approach does not work, has never worked, has never improved the livability or safety of a city, never brings the promised economic benefits, and invariably makes things worse, thereby necessitating more "urban renewal." Her analogy with the fools who drained blood out of sick people until they died is frighteningly apt.
If anything, she holds back; while she says that the decay of cities is not only far from inevitable, but has been "purposefully manipulated for a quarter century to achieve precisely what we are getting," she never asks who was manipulating it or why they were doing it. It was prescient of her to see, even in 1961, how a combination of banks refusing to lend money in cities, of tax money being funneled in buckets to automobiles, roads and suburbs, while cities were choked of financial aid, and of zoning and planning theories, would combine to create the disaster we have today.
She quickly runs through a history of modern urban planning, beginning with Howard's "Garden City" experiments in 19th century England, when cities really were seen as evil disasters needing to be broken down and rebuilt. Howard thought of planning as the creation of a static living environment, which should be protected from change or influence by its residents -- which works no better in cities than it does in software. She moves on to Le Corbusier, whose "Radiant City" visions of towers in parks led to the dreadful housing projects, and brings in Burnham's "City Beautiful" approach of segregating the great civic works of a city (government buildings, cultural institutions) from the city streets.
But she has little time for theories and instead returns to the practicalities of how actual cities work. Her overall point is that cities, when they function correctly, create their own order, and planners ignore that at their own peril, ending up with something even worse than ugliness or disorder: "the dishonest mask of pretended order, achieved by ignoring or suppressing the real order that is struggling to exist and to be served." 
She starts her actual analysis with the sidewalk, and what makes us feel safe in our cities. She begins with an interesting way to differentiate a city from a town or a village: "Cities are, by definition, full of strangers."  And therefore the question of safety is how to make people feel safe in a crowd of strangers. The answer has nothing to do with policing and everything to do with casual enforcement of standards, and those standards are enforced by the people using the street and those living there.
A safe city street, she says, has three elements: 
- A clear demarcation between public and private areas;
- eyes upon the street;
- continuous usage
In reaction many planners make things worse, trying to turn their precious planned communities into fortresses with gates and security guards. Hostility increases, the feel of the area gets worse and worse, and no one is really safe. Or they take refuge in vehicles (she compares this to drivers in a safari reserve) and the streets become even more deserted.
She concludes this chapter with one of the more famous sections of the book, in which she describes the give-and-take of a day on her block of Hudson Street in Greenwich Village. While somewhat idealized, it's instantly recognizable as how things work on a good city block. A block, one might mention, that Robert Moses tried to destroy with one of his expressways.
She continues with her discussion of the lowly sidewalk by discussing its effect on two things: contact between adults, and the rearing of children. A busy neighborhood sidewalk is a venue for multiple casual contacs with your neighbors, with local business owners, and with complete strangers. Cities are full of people that you'd never invite into your home or go out for dinner with, but that you do want to have an occasional conversation with. The sidewalk provides a place to do that at your own time, with an easy excuse to move on or to avoid someone you don't feel like talking to, and without any need for uncomfortable or inappropriate prearrangement. And out of these contacts come "a web of public respect and trust" with which you can tell someone misbehaving to stop, and know that someone will back you up.
She discusses the concept of privacy at length -- not "window privacy" which is easy to get, but the privacy of not having people know your business unless you want them to. A properly functioning city allows that privacy without leaving you entirely without a support system. She talks about the common urban habit of leaving a key with a local storeowner -- as she says, "a service that cannot be formalized." The corner deli provides a myriad of services like this as well as opportunities for contact. "It is possible in a city street neighborhood to know all kinds of people without unwelcome entanglements."  But in planned communities or housing projects, these institutions were deliberately destroyed, replaced with organized meeting places that have no social network to support them. The end result is that people isolate themselves defensively, everyone becomes anonymous, and no one feels safe telling the kids to stop misbehaving. [57,59,65]. This chapter is one of the wisest descriptions of city life I've ever seen, down to her discussion of the need for "self-appointed public characters" and the way that a business with too many customers can no longer provide those many services -- so that when zoning or planning restricts commercial to a few areas, creating unnatural monopolies, the businesses become impersonal and unfriendly. What makes this more remarkable is that she was writing at a time when most planners saw no value whatsoever in street life or neighborhood activity.
She becomes even more acerbic in her discussion of children, and what she calls the "superstition of planning and housing" that children playing on the street are worse off than those playing in nice well-tended playgrounds."  The problem with those well-tended places is that there aren't enough adults around, and children can then do horrible things to each other as they tend to when unsupervised. "Planners do not seem to realize how high a ratio of adults is needed to rear children at incidental play," she says. "Nor do they seem to understand that spaces and equipment do not rear children."  So the building of playgrounds (one of the activities, by the way, that is often cited as evidence that Moses was not all bad) "wastes this normal, casual manpower for child rearing and either leaves this essential job too much undone ... or makes it necessary to hire substitutes."
The myth that playgrounds and grass and hired guards or supervisors are innately wholesome for children and that city streets, filled with ordinary people, are innately evil for children, boils down to a deep contempt for ordinary people.She also points out that most of these planned play areas are boring, aimed at "filling the presumed daily needs of impossibly vacuous housewives and preschool tots" . "No child of enterprise or spirit will willing stay in such a boring place after he reaches the age of six." 
Older children are noisy and energetic, and they act on their environment instead of just letting it act on them. Since the environment is already "perfect" this will not do.She ends the chapter with two interesting points. One is that these planned places are essentially matriarchies, and that segregating work and business areas from play areas mean that men are not usually involved in the rearing of children.  Also, the widening of streets for cars, and the resulting narrowing of sidewalks, makes them inhospitable for play. A thirty-foot sidewalk, she says, has room for trikes and jump-rope and a million other activities, especially if the building line is not even -- play happens in the niches. And the incidental play she considers so important isn't something that happened at preplanned times, but rather in the spare moments of a child's life, before being called in for dinner or on the way home from school.
From sidewalks, she moves onto parks, specifically neighborhood parks. She starts with the premise that parks are not an automatic benefit to a community, that they need benefits from the surrounding community in order to work, and without those benefits, they become like the "dozens of dispirited city vacuums called parks."  The veneration of open space (which she compares the veneration of magical fetishes) never questions who uses the space, or what they use it for, or when they use it. The requirements for a park to work are basically that there be a wide mix of uses around it, so the park is used by a variety of people, all with different schedules. This way it remains busy all the time. And variety, as she says, attracts variety.
She's merciless in her criticism of the process then in vogue (driven, of course, by Robert Moses) of tearing down sections of city neighborhoods to build parks. "There is no point to bringing parks where the people are if in the process the reasons that people are there are wiped out and the park substituted for them."  She ridicules the notion that parks are "the lungs of a city" since trees cannot recycle anywhere near as much carbon dioxide as is produced by a city neighborhood, and in fact, more open space means more sprawl means more pollution, so in a way, badly planned parks can have a negative effect on the environment. 
The park itself needs a few things in order to succeed:
- Intricacy -- room for different moods and activities, a feeling that there's something worth exploring, "subtle expressions of difference." 
- Centering -- the park should have a central place that most paths lead to.
- Sun -- people avoid shade, one of the many reasons for the abandonment of the dismal midtown "plazas" built by office building developers to get some extra stories on their buildings.
- Buildings -- a park needs boundaries, and people nearby to use it. A park next to a vacant lot or a parking lot just won't be used.
She wraps up Part I with a discussion of neighborhoods, and how they need to be richly interconnected. "This 'ideal' of the city neighborhood as an island, turned inward on itself," is completely unrealistic. "It leads to attempts at warping city life into imitations of town or suburban life." [115,112] A small town may be the same size as a neighborhood, but the people in a small town work together, shop together, their children attend the same schools -- they're connected by geography. City residents are not. Their connections extend across the city to many differing communities, and they do not want to "face inward." Yet, the city neighborhood is a critical part of self-government, so it must be planned in a way that's inclusive, that overlaps with other neighborhoods, that gives residents many reasons and venues to meet each other and interact.
She then discusses the cooperation of neighborhoods to form districts (her own Greenwich Village, for instance) which are necessary to mediate between the city itself and the neighborhoods, which are too small to have any political power on their own. She concludes with a basic set of prescriptions for good neighborhoods:
- Lively and interesting streets;
- A continuous fabric of such streets
- Parks and squares and public buildings that are part of this fabric
- Functionally identifiable districts, a result of the first three, and what she calls the "cross-use" that interesting and varied streets will encourage.
Like The Timeless Way Of Building, this is a warmly human book. It looks at how we live, and recommends building nurturing cities that support people, rather than brutal cities that negate their efforts.