"The Waning of the Middle Ages" is a historical analysis of the cultural life of the late Middle Ages, particularly in France and the Low Countries, during the 14th and 15th centuries. It delves into the period's modes of thought, forms of expression, religious beliefs, and social norms. The book argues that the era was characterized by a highly stylized and overwrought civilization, marked by an excessive emphasis on chivalry and courtly love, a religious mindset dominated by the fear of death and the afterlife, and a cultural milieu that was both highly imaginative and deeply pessimistic.

"Homo Ludens: A Study of the Play-Element in Culture" is a comprehensive exploration of the significance of play in human culture. The author argues that play is not just a childhood activity but a crucial component of societal development and cultural evolution. He delves into various aspects of culture such as law, war, knowledge, poetry, and philosophy, demonstrating how each has been influenced by elements of play. The author's thesis is that understanding the role of play in our culture is essential to understanding human nature itself.