Leo XIII's encyclical on the relationship between capital and labor (Rerum Novarum) and Abraham Kuyper's speech to the first Christian Social Congress ("The Social Question and the Christian Religion"), both published in 1891, are foundational sources for subsequent Christian social thought in their respective traditions-Roman Catholic and Reformed. This volume, in celebration of the 125th anniversary of these two landmark publications, includes authoritative English translations of these works and an introduction that outlines their context and significance. The thought of these two theologians-one an Italian scholar-pope and the other a Dutch Reformed pastor, professor, and politician-provide enduring wisdom for developing and articulating a Christian witness in the modern world.