Written for the ninetieth anniversary of Rerum Novarum, this encyclical on human work argues that work is not first an economic quantity but an activity of the person: because the worker is a subject made in God's image, labour has priority over capital and no economic system may treat the worker as an instrument. John Paul II examines work in the book of Genesis, the conflict between labour and capital, the rights of workers (just wage, rest, association in unions, the situation of the disabled and of emigrants), and closes with a spirituality of work rooted in Christ the carpenter and in the Cross.