The purpose of this book is to set forth the principles which ought to govern the planning of buildings with respect to sunlight, a subject to which very little attention has been given.<br><br>Several years ago, in an essay on hospital construction, I wrote as follows: "To study properly the question of sunlight, a sun plan of the buildings must be drawn, and their positions considered with respect to the shadows they cast upon each other and upon the ground". This statement describes very well the general method of study which I have followed in my investigations, the results of which are now for the first time presented to the public in a complete form.<br><br>I had begun my study of orientation with hospitals especially in mind, but I soon realized that the general principle of planning with reference to sunlight was of fundamental importance in the design of all buildings, and especially in the planning and laying out of cities.