First of all, this book should be a romance – we have a dashing hero and a gorgeous heroine who are terribly, terribly in love. However, the intervention of World War I spoiled this ideal romance. With this party pooper in the equation, the focus ends up being on the "terribly" part, rather than the "in love" part. The Jake-Brett relationship can never happen, due to Jake’s war wound, so the rest of the novel attempts to create other relationships to replace it (Brett-Cohn, Brett-Mike, Brett-Romero), but it never works out.
The book can also be defined as a Modernist Novel. It’s not as classic an example as, say, Ulysses, but it’s still often lumped in this genre. Hemingway made a conscious move away from the conventions of the nineteenth century novel, attempting to create a new voice for the new world of the postwar twentieth century. We think he succeeded – what about you?