Behavioral psychology is a branch of psychology that focuses on understanding and explaining how behaviors are learned, modified, and maintained through environmental influences. It is also known as behaviorism or the study of behavior. The main goal of behavioral psychology is to determine what motivates people to act in certain ways by looking at their environment and experiences.

Behavioral psychologists use various methods to study human behavior, including laboratory experiments, observational studies, surveys, questionnaires, interviews and case studies. Through these different techniques, they can observe patterns in the way humans behave in order to gain an insight into why they do what they do. This knowledge can then be used to create interventions that modify behavior for improved outcomes or simply just better understand behavior from a scientific perspective.

The history of behavioral psychology dates back centuries; however, its modern development began with the work of John B Watson, who established it as an independent field of study during his famous 1913 lecture, "Psychology as the Behaviorist Views It." In this lecture, Watson introduced his now widely accepted definition of behavioral psychology: "the science which deals with observable phenomena alone" (Watson). This meant abandoning introspection, or studying one's own thoughts, as a valid research tool because it could not be observed objectively, unlike like physical actions, which could be observed externally via direct observation or indirectly via self-reports such as surveys/questionnaires.

From this foundation, more specific theories were developed, including classical conditioning by Ivan Pavlov, wherein associations between stimuli result in predictable responses; operant conditioning by Burrhus Frederic Skinner, whereby voluntary behaviors are shaped through reinforcement or punishment; and social learning theory by Albert Bandura, where behavior is shaped by the modeling of others' behaviors combined with cognitive processes such as attention and motivation. Additionally, there are information processing models that focus on mental representations built up over time based on incoming data, and evolutionary approaches that explore how genetic inheritance affects our current choices today. All these topics form part of modern-day behavioral psychology. However, there have been many other developments since then, such as the recent emphasis being placed upon neuroscience. These developments all aim to better understand what drives us internally behind our conscious decision-making process, thus enabling us to make healthier choices, both individually and collectively, benefiting society overall.

In conclusion, we can see that throughout history, behavioural psychologists have worked hard to comprehend why people behave they way do. They have used methodologies ranging from simple observations to complex testing techniques, all leading towards creating effective interventions that help individuals lead better lives while providing researchers with greater insights into human behaviour. This in turn allows them to develop new treatments targeting particular disorders, ultimately improving public health standards globally.