The spirituality of Saint Clare of Assisi, the soul mate of Saint Francis, is the object of this book. Her spirituality was inspired by Francis' and she owes much to him, like he to her. This book is meant to be a contribution to the study of Clare and her thoughts. In her four letters, written to Saint Agnes of Prague, Clare expresses herself more openly about her deepest motivations than in any other writing. They concentrate on the heart of her choice of life and as such they reproduce the most beautiful gift which God gave her. Clare's sprituality as it comes to the fore in these leters, can only then be fully understood when we take into account their creative structure. The specific aim of this books is to do justice to her texts in a method which, to our knowledge, was never applied before. It consists in an elaborated analysis of the fine, concentric structure of the letters to Agnes, combined with an ongoing commentary in which historical data are also given attention.