Mater et Magistra is a papal encyclical written by Pope John XXIII which was promulgated (issued and widely distributed) on May 15th, 1961. The literal translation of the title is Mother and Teacher, but the title accompanying official English translations is On Christianity and Social Progress. The historical context is clarified by Pope John, along with his reasons for writing it, in the body of the encyclical. First of all, he intended it to be a follow-up and clarification of points brought out in two previous encyclicals: Rerum Novarum, or Rights and Duties of Capital and Labor, promulgated by Pope Leo XIII on May 15th, 1891; and Quadragesimo Anno, promulgated by Pope Pius XII on June 1st, 1941. Both of these previous encyclicals had to do with Catholic social teaching, and Pope John summarizes and explains these encyclicals at the beginning of Mater et Magistra.

Following these summaries, Pope John goes on to clarify the historical context that prompted him to write Mater et magistra. This explanation of historical changes that made a new encyclical necessary is in paragraphs 46–50 of Mater et Magistra. He states that "the economic scene has undergone a radical transformation, both in the internal structure of the various States and in their relations with one another."

In the fields of science, technology, and economics, Pope John mentions the emergence of nuclear technology (both for war and peace), "chemistry in the production of synthetic materials," automation, "modernization of agriculture," communications such as radio and television, improvements in transportation, and "the initial conquest of interplanetary space."

In the social field, Pope John points to the emergence of social insurance, social security systems, labor unions, and improvements in basic education. He also says that there is "a marked disparity in the economic wealth possessed by different countries."

In politics, Pope John states that in numerous countries "citizens are taking an active part in public life." He emphasizes "the breakaway from colonialism and the attainment of political independence" of African and Asian peoples, and the interdependencies of modern nations.

All of these changes were taking place on the international scene in the early 1960s, and in the historical context of an era that witnessed these changes, Pope John felt that he had to write this new encyclical as "a torch to light the pathways of all who would seek appropriate solutions to the many social problems of our times."

After presenting this historical context for the writing of his encyclical, Pope John goes on to delineate specific ways in which struggling industrial and agricultural workers can be assisted through modernization, the creation of improved infrastructure, the establishment of price protection, and other means. He calls on wealthy nations to assist poorer nations, but without imposing control or disrespecting local cultures.