A very good, very concise (just 290 p long) summary of the main conceptual contributions and historical-academic lineage that made up the four main traditions of social theory in the author's view, until the mid 1980s: the conflict tradition, made up of the descendants of Marx/Engels and Weber; the American microinteractionist tradition including the symbolic interactionists, ethnomethodologists, and Goffman; the Durkheimian tradition(s) of functionalists Parsons and Merton and British Bernstein and Mary Douglas (whom I had read previously and understood next to nothing, really); and finally the almost strictly quantitative-based utilitarian/rational tradition (the whole talk of Kenneth Arrow, rational choice, bounded rationality, and the whole of economics-like thought in sociology).
These four "traditions", as Collins is the first to admit, are convenient fictions. Still, he claims they are clearly visible, for instance, in the geographical distribution of researchers under their umbrella - conflict in Germany, microinteractionists in America, Durkheimians in France and Britain, and utilitarians in Britain (with everything mingling together in the US at the late 20th century). I found this particular claim to be flimsy, or, more specifically, of little explanatory value. At least in the case of Weberians and Marxists, which Collins claims wouldn't recognise themselves under the same tradition, I'd claim what unites them is precisely their competition for a similar mode/levdl of description (I was going to write market, and indeed I'd say there are markets among intellectuals for very different levels of description, just as there are are for political leanings, and the latter do not always go together with the former in the same combinations), that is, that of the conflict between different groups (be it organisations, classes or nations), with less relative importance to the individuals interacting that together somehow make up these larger structures. Relative, that is, to the microinteractionist tradition, which again also may be seen as competing for the same clientele as the symbolic interactionists and the ethnomethodologists (hence their mutual attacks on one another over time). The same principle can't be applied to the so-called Durkheimian tradition, whose three main offshoots mostly have in common only their intellectual forebear, but it most definitely applies to what Collins dubs the utilitarian or rational tradition. The mode of thinking associated with this latter tradition, that of statistical research in general and seemingly predominant in political science and economics in particular, has a tremendous appeal in today's society, drowned as it is in numbers, which are contested as much as they are seen as paths to our salvation (look no further than the number-based public debate surrounding measures against covid-19 right now), and it is no wonder research under it has grown incredibly in the decades since Collins' book - quantitative research is perceived as much more scientific, intuitive, and appealing to the average intellectual (esp outside the humanities) today than the boatload of concepts connected to very intricate and unique philosophies which are often seen to make up works based on Marx, Weber, or Durkheim.
Collins writes very clearly, which is of course a bit deceptive at times. Perhaps because the book intends to cover dozens of authors in so few pages, he can't help but be superficial at times, such as in his treatment of then-burgeoning Bourdieu (which, from this book, all we learn is that he was a French sociologist combining Durkheim with the conflict tradition).
It is already a very dated book - the 1994 2nd edition in fact is an expanded edition from the 1984 1st ed, which didn't include a chapter on the rational/utilitarian tradition. That is almost forty years ago, and a lot of authors which were just starting to become famous then such as Bourdieu, Latour, Habermas, and Luhmann are mostly missing from Collins' presentation.
The most important contribution of this book for me, a starting scholar in sociology (of law), was the historical overview Collins constructed of the (then) major names in social theory. He helped me locate (literally, there is a table for each chapter) authors whose names I had heard in very different places in a same grid, and to see exactly who connected to whom and in what order (something I consider particularly basic in comprehending any scientific tradition). I'm sure anyone interested in getting a broad but rather superficial look of "what is there" in social theory will enjoy this book.