The Selection is the story of the life of a 16-year-old subject of Illéa, America Singer. In the monarchy of Illéa, formed out of the remnants of the USA in a post-apocalyptic world, a strict caste system restricts freedom and condemns most of the subjects of the monarchy to lives of poverty. In this system, one's caste determines which kinds of professions those in it can dedicate their lives to. For those in the lower castes, this means being denied an education and being forced into positions of servitude. It is nearly impossible to rise in the caste system. The only means of doing so are amassing immense amounts of wealth or participating in an advantageous marriage. Women take on the caste of the men they marry.
America Singer is a member of the Fifth caste, which was made up of artists who rely upon the financial support of patrons of higher castes. The Singer family struggles to meet their basic needs in the Illéan economy. America is a singer and is also proficient in a number of instruments, particularly the violin.
Political struggle is a constant fact of life under the monarchy. The royal family works to maintain their hold on power in order to keep the peace within Illéa's borders. There exist two rebel groups, one in the North and one in the South, that routinely stage attacks on the palace in the pursuit of an unknown goal.
When America receives a letter from the crown prince of Illéa, inviting her to take part in the Selection process, a televised competition where 35 girls are chosen at random to compete for the hand of the prince in marriage, initially she resists signing up. America is convinced to put her name into the drawing by her secret boyfriend, Aspen, and her mother, both of whom know that participating in the competition will secure America and her family a better life.
When, to everyone’s surprise, America is chosen, she has to travel to the palace and compete for the love of a man she disdains. But over the course of the competition, America develops a friendship with the prince due to her candid nature and his compassionate disposition, and she vows to help him decide which of the girls to marry. In turn, the prince vows to keep America in the competition until the final three. Although the prince develops feelings for America, she routinely denies his advances due to her love for Aspen. In the palace, America gains friends in some of the other Selected, and enemies in others. She challenges the inequality that the elite of Illéa have taken for granted, and opens Prince Maxon's eyes to the suffering his subjects endured. A conversation the prince has with America about the hunger she routinely has to endure as a Five encourages Maxon to institute a food assistance program for the lower castes.
Rebel attacks on the palace inspire fear among the contestants. The royal family utilizes the attacks to divert attention from their failings as leaders in Illéa. They believe that the rebels' attacks are meant to weaken the image of the monarchy and therefore weaken the state itself.
America decides to allow herself to be courted in earnest by Maxon after he gives her his first kiss. Soon after this, Aspen arrives at the palace as a guard after being drafted into the army. America and Aspen resume their relationship in secret. When rebels attack the palace again, America realizes her ability to use her newfound authority in order to protect her maids. After the attack, the prince narrows the competition down to the last six girls, the Elite, and America is one of them. He tells America that she would be his automatic choice if she were not unsure of her feelings for him. America now feels empowered to end her affair. The book ends with America deciding to actively participate in the Selection as a competitor for the first time.
