The classic that triggered the movement to study and document the collapse of "social capital" - obligatory and reciprocal social relationships that build through more regular human interaction with neighbors as well as in groups like bowling leagues (hence the metaphor in the title) and civic groups. By the end of the last decade, arguments for strategies and interventions that would augment "social capital" in both individual and communities were vogue in grant applications, showing how quickly Putnam's ideas became institutionalized.
I've used an excerpt of this in my Intro. SOC class for a decade now and it's helpful for students to understand the context for the increasing alienation and dysfunction they feel in their own lives, especially when supplemented with the data that over a quarter of U.S. adults can name not a single friend and social isolation is a huge problem (and increasingly pointed to as a cause, not a consequence, of substance abuse and mental health problems.) There is also data from "gated communities", the phenomena separating the "haves" from the "have nots" around the world, that while residents naturally list security as a top attraction, "knowing your neighbors" was another top-listed reason, then many apparently drew a blank when later in the survey were asked to list neighbors they knew by first name. Only a small number listed even one. (This was a sociology study of gated community residents in Houston, TX, that was one of the original cities that started gated/locked communities. Of course, those Houstonites knew that their neighbors weren't brown or black skin, generally, so we know what is important about our neighbors in gated communities - they are wealthy and white!)
Putnam is a good Liberal and no radical, but I can't help think that he didn't simply document what Marx predicted long ago, that capitalism would lead to alienation of self from others as well as from ourselves.