Recent years have witnessed a proliferation of studies devoted to medieval Hebrew science, but few editions and explications of texts. In this book, Ruth Glasner provides a critical edition and exhaustive analysis of two polemical letters pertaining to physics by the fourteenth-century Provençal poet and philosopher Jedaiah ha-Penini (Bedersi) (born ca. 1285). These letters were largely forgotten until S. Pines drew attention to their significance and called for their publication over thirty years ago. That call has been answered in exemplary fashion in the present volume.