The central theme of Herland is defining gender—the roles, how it is socially constructed, and how it is viewed as unchangeable by both genders. The idea of defining genders begins when the men first meet the women of Herland. In comparison to the women of their world, the men view the women of Herland to have masculine physical features: having short, functional hair and lacking curves. The women are physically strong and demonstrate this by building huge buildings in their country. Along with the women having masculine traits—as the outside world perceives—Jeff is in some ways feminine despite being a male. Jeff’s gender has a conflict of interest with the men he travels with to Herland. Jeff's feelings mirror the women’s feelings of Herland rather than the men. At one point, Van feels betrayed by Jeff’s emotional responses and agreements paralleled with the women.
Another central theme of the novel is motherhood. The all-female society operates heavily surrounding the child-rearing process. They even developed and modified their language over time in order to make it as simple as possible for the children to learn, education being one of the most important aspects of the culture. Each mother submerges her one child completely with the love and affection of the whole community for the first two years of life until it is taken upon the most equipped few to further their education. One of the male explorers is surprised to hear that the women would give up their children to the care of another, but the women explain that children are taken as the responsibility of the whole community and not just that of the biological mother.
The book also focuses on individuality by the way that each child is given her own unique first name with no need of last names. The Herlanders keep a detailed history of their lineage and they see no need to claim ownership over their child by instilling their own name upon that child the way the culture of men is used to. The women are able to love openly without forcing insubordination upon others, not excluding their offspring.
Jeff is one example of how Gilman represents a feminist voice. As a feminist writer, Gilman provides an additional outlook on women and their roles during her time. She demonstrates her praise of women being independent of men. Gilman creates a means of equality to the men and at times conveys a theme of being superior to the men. In contrast to the world where the men came from, they feel weak compared to the women of Herland. The women are conveyed as kinder and smarter than the men, as determined by the narrator. The women are smart by means of surviving when they are cut off from the rest of the world. They live in a country where they "breed-out" (kill off) parts of nature if it is a strain on their society, i.e., cattle, dogs, and certain types of butterflies. In addition to breeding-out parts of nature, the women of Herland will breed-out girls in their society who are defiant and not virtuous; they will not let girls of Herland reproduce.
Education is the "highest art" in Herland and has been the reason why the country has thrived. Based on Maria Montessori's principles, education is not force fed as it is in the men's world. The theme of education is of utmost importance and highly valued.
When the three male characters are imprisoned by the Herlanders, their hair grows long, which Gilman does to symbolically link them to womenkind. Throughout the novel, Gilman reverses the stereotypical gender roles: the women have short hair, the men have long hair; the women teach while the men learn; the women are physically stronger than the men, etc.
There is an undercurrent of racism and praise for eugenics in the book. Gilman consistently refers to the people living to in the valleys below Herland as “savages” and presents no evidence to substantiate this claim. As for eugenics she seems to believe that character “flaws” can be bred out of humanity as she repeatedly states that only the most virtuous women are allowed to enjoy the gift of maternity. The book describes a women-based Utopia, the last two boys dying, leaving only females to create an extremely elistic civilisation. However, the arrival of the three explorers is regarded as a blessing, allowing the Herland citizens to get back to a bi-sexual society.