Matroid theory is a relatively young field of mathematics. Its origins are in 1935 when Whitney generalized common graph theory and linear algebra principles. This book was first published in 1992 and it is in recent times the most complete introductory monograph on matroid theory. Since the topic has grown widely one cannot give a complete survey in a single book. Hence the author has had to be selective. The first few chapters were chosen in a natural way. Chapters 1-6 provide a basic overview of matroid theory and cover the materials needed for this introductory course on the topic. The later chapters contain more details on matroid connectivity, representativity and decompositions. The theory is built stepwise and proofs are presented for almost all important statements. Hence the reader gets an overview of the results and can also observe how the proof techniques work. From this point of view, the book is essential for the researcher but can also be used as a textbook for both introductory and advanced courses on matroid theory. The advantage of the book as a study text is that it contains many examples and each section is supplemented by exercises.