From the title, readers would assume that the novel is centered upon the theme of a dynamic friendship. And, while the friendship between Lila and Elena is certainly the central focus of the novel, it is not always as positive as one would expect. The friendship challenges both girls and propels them to decisions and actions that define their lives. While the two girls' lives take very different turns, the impact of their friendship on each other is unmistakable.

Another theme present in this book is class (socio-economic status). Throughout the novel, the different social classes of the girls and their families are examined. Both Lila and Elena strive to move from the struggling, lower-middle–class of their childhood, but each does this in a different way. Lila ends up quitting school at an early age, helping with the family business, and marrying, even though these decisions mean personal compromise and disappointment to her. Elena succeeds in gaining a formal education and flourishes as she travels and becomes more modern. However, she is never completely satisfied with her accomplishments.

Gender is another important theme. As the novel is set in Naples, Italy, in the 1950s, it is clear that girls growing up in the post-war period are somewhat limited in educational and professional opportunities. Cultural and familial expectations of the girls are prevalent throughout the novel. Both girls fight feelings of inferiority in regard to the dominant men in their lives, as well as each other, at times.

Also, an ever-present theme in the novel is envy. From an early age, Elena and Lila compete in almost every arena, including looks, education, popularity, and accomplishments. Lila, who is intelligent, is jealous of Elena's ability to continue and complete her education; Elena is envious of Lila's courage, as well as of her ability to read people and interact intuitively with them (especially men). While the women are the main characters, the novel also explores jealousy in the community, as some are envious of the brothers in the Solera family when they prosper and can afford nice things.