This collection of lectures by Fields Medalist L. Nirenberg provides a comprehensive introduction to the theory of strongly elliptic partial differential equations. The book covers topics such as the Dirichlet and Neumann problems, regularity theory, and Hörmander's theorem. The author presents the material in a clear and accessible manner, making it an ideal resource for graduate students and researchers in analysis.This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it.This work is in the "public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work.Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.