Many textbooks have been written to describe a power system operating under balanced or normal conditions. A few texts also deal, at least in an elementary manner, with the unbalanced system conditions. The primary object of this book is to provide a text to be used by graduate students and to challenge the student to draw upon a background of knowledge from earlier studies. Since this is intended for advanced studies, the student reader should be able to use circuit concepts at the advanced undergraduate or beginning graduate level and should have a working knowledge of matrix notation. Particular stress here is placed upon a clear, concise notation, since it is the author's belief t h a t this facilitates learning.