Human Behavior Theory is a graduate to doctoral level text for courses on human behavior in the social environment. These courses are offered as either advanced HBSE courses in master's programs or doctoral programs. They focus on understanding the various theories surrounding human behavior in much greater depth than introductory level HBSE courses. In this text, the authors use a critical thinking approach to engage students to think differently about theory. The book is divided into three sections. The first part focuses on introducing theory (what it is and what it is not). Then the next chapter outlines the various theories that will be covered in the text, including developmental theories, environmental theories, diversity theories, systems theories and emerging theories. Then chapters 3-8 looks at each theory in detail. Section II then applies each theory to social work practice. The authors conclude with a chapter that ties it all together. This book is unique in its expanded coverage of theories related to diversity (including race, gender, sexual orientation, disability, and religion) and its focus on getting students to think critically and differently about theory.