This volume consists of over one-hundred epistolary exchanges between Martin Heidegger and one of his earliest students, Karl Lwith, who became a renowned and accomplished philosopher in his own right. The letters span a period of just over fifty years and range from casual to philosophical in tone. The more philosophically oriented letters shed important light on the ideas and writings of both Heidegger and Lwith, while the more casual letters provide insight into Heidegger the teacher, the man, and the friend, as well as into Lwith the devoted but reflectively critical student. By providing previously untranslated materials, this volume contributes to a greater understanding of the lives and the work of these two crucially important philosophers. Additionally, through the various bibliographical and cultural details that are disclosed along the way, this volume contributes to a greater understanding of German intellectual and cultural history during the span of its most challenging and devastating years.