Universal Algebra

Universal Algebra, heralded as ". . . the standard reference in a field notorious for the lack of standardization . . .," has become the most authoritative, consistently relied on text in a field with applications in other branches of algebra and other fields such as combinatorics, geometry, and computer science.
Each chapter is followed by an extensive list of exercises and problems. The "state of the art" account also includes new appendices (with contributions from B. Jónsson, R. Quackenbush, W. Taylor, and G. Wenzel) and a well-selected additional bibliography of over 1250 papers and books which makes this a fine work for students, instructors, and researchers in the field. 
"This book will certainly be, in the years to come, the basic reference to the subject."
--- The American Mathematical Monthly (First Edition)
"In this reviewer's opinion [the author] has more than succeeded in his aim. The problems at the end of each chapter are well-chosen; there are more than 650 of them. The book is especially suitable for self-study, as the author frequently provides ample explanation not only of what he is proving, but also of how and why he is proving it. As a reference work for the specialist or a text for the student, the book is highly recommended."
--- Mathematical Reviews (First Edition)
"Since the first day of its appearance in 1968, this book has been the standard reference in universal algebra, and no book since has reached its quality."
--- Journal of Symbolic Logic (Second Edition)