Wide Sargasso Sea is a novel in three parts. It belongs to a number of genres and can be described as postmodern in form. Some of the novel's postmodernist aspects include Rhys's intertextual point of departure, the varied narrative voices, the political themes, and the deconstruction of truth as a stable, attainable ideal.
In line with its political themes, the novel can be categorized as both postcolonial and feminist. Associated with the mid- to late 20th century, postcolonial literature tends to feature a subversion of traditional colonial discourse. Although one can label texts from many centuries ago as "feminist," feminist literature is often associated with feminist movements of the 19th, 20th, and 21st centuries. In the 1960s, when Rhys was working on Wide Sargasso Sea, the second-wave feminism movement swept the Western world. It's possible to describe Rhys's core project as both postcolonial and feminist, as her main motivation was to give the creole madwoman in Jane Eyre a story and a voice. Throughout the novel, she examines the postcolonial and patriarchal discourses that are latent in Charlotte Brontë's narrative and the world more broadly.
Since another novel was the jumping-off point for Rhys, Wide Sargasso Sea can also be categorized as a parallel novel. Related to pastiche, parallel novels are works that an author derives from another work—and sets within the same fictional universe. Borrowing not only characters and settings from Jane Eyre, Rhys also conjures up Brontë's gothic atmosphere. This sort of referential mode is what postmodernist literary theorists call intertextuality. It is worth noting, however, that even if Rhys was active a century after Charlotte Brontë, Wide Sargasso Sea is meant to serve as a prequel to Jane Eyre. Only the brief third part of Wide Sargasso Sea overlaps with the time frame of Jane Eyre.