This is the first summary I've attempted to write myself. I just hope it's more understandable than the original text. It's important to note that this text was published in 1987, compared to Gayle Rubin who wrote in 1975, Judith Butler in 1990 and Christine Delphy in 1993.
Whilst this text may have been a while aften Rubin wrote her ideas, it's considered to be an earlier work on the subject of gender. It's also a relatively common reference in later works on the subject, in which the authors expect you to know what they're referring to.
Zimmerman and West quickly introduce their main proposal, that gender is "done", rather that being exclusively a social role or representation of a society. Gender is also not an individual thing, but "an emergent feature of social situations" (p.126). Although the idea of gender as something perceived is not new, the focus on the constant behavioural aspects and interpretations of those adds a new way of viewing gender.
They also introduce three definitions, which are:
Sex - "Sex is a determination made through the application of socially agreed upon biological criteria for classifying persons as females or males." (p.127). The authors note that criteria such as chromosomes and genitalia do not always concur about which sex the person should belong to, although they do not develop the idea of sex as a social construction as far as later authors do.
Sex category - This is which category of sex an individual is placed in due to what West and Zimmerman call "socially required identificatory displays" (p.127). I believe they are referring as much to appearances as attitudes, as when we try and interpret someone's sex we tend to look at things like face, hair, and clothes more so than how someone acts.
Gender - This is based on how we act compared to societal norms for our sex category, and serves to bolster our membership to one or the two sex categories. Such activities and attitudes emerge from our sex category.
West and Zimmerman then argue that gender is not merely a role. This is because a role always depends upon situation, whereas gender is the same in any situation. In addition, they argue that gender is not merely a display, as this language implies a not so fundamental and somewhat limited element of interaction.
An interesting case study the authors bring up in relation to their theory is that of Agnes; a transexual who was raised as a boy, yet adopted a female identity at the age of 17. Since Agnes was brought up as a boy, she had to consciously learn how to act like a women, learn to comply the the socially expected ideas of femininity. West and Zimmerman note that we have a natural desire to determine the sex category of a person, and are disturbed if we fail to be able to do so.
Another area brought up is the division of labour. At least around the period of 1985, Sarah Berk noted that even with a married couple both working, the wife tended to do the majority of housework and child-care tasks, and more oddly discovered that both husbands and wives believed the arrangement to be fair. West and Zimmerman essentially see this as another display of manly and unmanly roles, to do otherwise would be to be doing another gender to the one that person wishes to do. Here, the authors point out the existence of the dominant and subordinate statuses of the sex categories. They explore this further in commenting that doing gender as dominant and subordinate reinforces and legitimates the current social structures and arrangements.
West and Zimmerman conclude that social change needs to be pursued at a cultural level as well as an institutional level, as it is difficult to change a structure that automatically reinforces itself.
This work does not appear as particularly novel, but it does rationalise something we do instinctively, even if we realise whether we are doing it or not on a conscious level. The idea of sex categories does bring in an important idea, as it explains why someone who we clearly identify as male, however they may act, cannot escape the initial male identification, although with our gender perception we will consider them to be unmanly, but most importantly still a man.
The story of Agnes shows that gender can be learned, but it also shows it can theoretically be unlearned. West and Zimmerman clearly don't see the logic in someone being unable to fully express themselves as they wish due to knowledge of how other people will interpret that.