Hugo Münsterberg was a German-American psychologist. He was one of the pioneers in applied psychology, extending his research and theories to industrial/organizational (I/O), legal, medical, clinical, educational and business settings. Münsterberg experienced immense turmoil with the outbreak of the First World War. Torn between his loyalty to the United States and his homeland, he often defended Germany's actions, attracting highly contrasting reactions.

Applied psychology is the use of psychological methods and findings of scientific psychology to solve practical problems of human and animal behavior and experience. Educational and organizational psychology, business management, law, health, product design, ergonomics, behavioural psychology, psychology of motivation, psychoanalysis, neuropsychology, psychiatry and mental health are just a few of the areas that have been influenced by the application of psychological principles and scientific findings. Some of the areas of applied psychology include counseling psychology, industrial and organizational psychology, engineering psychology, occupational health psychology, legal psychology, school psychology, sports psychology, community psychology, neuropsychology, medical psychology and clinical psychology, evolutionary psychology, human factors, forensic psychology and traffic psychology. In addition, a number of specialized areas in the general area of psychology have applied branches. However, the lines between sub-branch specializations and major applied psychology categories are often mixed or in some cases blurred. For example, a human factors psychologist might use a cognitive psychology theory. This could be described as human factor psychology or as applied cognitive psychology. When applied psychology is used in the treatment of behavioral disorders there are many experimental approaches to try and treat an individual. This type of psychology can be found in many of the subbranches in other fields of psychology.