Seinlanguage is a book of observations exploring the mundane routines of everyday life through the humorous eyes of Jerry Seinfeld. The book covers everything from dating to traveling to friendship. Seinfeld includes such things as the tension that often occurs on a first date to the comfortable rapport between his parents, married for many years. This book is entertaining, written much like Seinfeld's standup comedy, and allows the reader to visualize Seinfeld delivering the jokes in person. It is a book all of Seinfeld's fans are sure to enjoy.

Dating is a difficult situation that Seinfeld likens to a job interview. A couple must move into a relationship while learning everything about each other, rather like owning a new car without the benefit of an owner's manual. Eventually the relationship ends and the couple is left with the pain of hurt feelings. Seinfeld thinks this could be avoided with cards, such as those from a children's game, which would allow a person out of a relationship for free. Personal maintenance is another aspect of human nature Seinfeld finds amusing. The differences between the way a woman takes care of herself versus how a man does are numerous. Seinfeld thinks that women have a great way of shopping for clothes that men do not share.

Seinfeld next focuses on friendship, discussing how men have relationships contingent on the next pretty girl that comes their way. Seinfeld also discusses gift-giving, friends he does not want, and the awkwardness of having friends with new babies. In "Shut Up and Drive," Seinfeld shares his observations on travel, including car travel, the subway, and airplanes. Seinfeld speaks directly to airline attendants in the end of the chapter, begging them to please stop waking passengers up in order to serve them food.

In "Job Security," Seinfeld admits he has never held a proper job himself, but explores his observations of various occupations. Seinfeld seems to like law enforcement best, thinking how cool it would be to have the authority to tell people when they have done something wrong. Being a clown is at the bottom of Seinfeld's list and unemployment is the most difficult job, according to Seinfeld's observations. In "The Thing is the Thing," Seinfeld explores people's need to own stuff. Seinfeld talks about money, about theft, and about the media, particularly television. Seinfeld finds television to be most entertaining, although he does not like shows that are "to be continued" and public service announcements.

"Out and Back" is a chapter in which Seinfeld explores things he does outside of his home and things he does inside. Seinfeld talks about trips to the movie theater, sporting events, and the opera in the first half of the chapter, while the second half centers on his personal habits inside his apartment, such as his compulsion to be neat, but his dislike of cleaning. In the final chapter, "The Ride of Your Life," Seinfeld explores life in general, beginning in childhood, through the influence of parents, to the final steps in a person's life. Seinfeld sums up neatly, describing death as a person's need to move often and search for boxes, the final box being a person's coffin.