This book is based on parts of lecture courses for graduate students and advanced undergraduates in hydrodynamics, soft matter physics, and materials science. The subject of the book has never been presented as a whole in a single text. Unlike other books in the field, this text covers completely and at an elementary level the subject of defects, which has become very important in the last few years. The coherence of the present project is in its particular stress on the concepts of order & disorder.