History
The root of the word psychology (psyche) means "soul" or "spirit" in Greek, and psychology was sometimes considered a study of the soul (in a religious sense of this term), though its emergence as a medical discipline can be seen in Thomas Willis' reference to psychology (the "Doctrine of the Soul") in terms of brain function, as part of his 1672 anatomical treatise "De Anima Brutorum" ("Two Discourses on the Souls of Brutes").

Until about the end of the 19th century, psychology was regarded as a branch of philosophy.

In 1879 Wilhelm Wundt founded a laboratory at the University in Germany in Leipzig specifically to focus on general and basic questions concerning behaviour and mental states. William James later published his 1890 book, Principles of Psychology which laid many of the foundations for the sorts of questions that psychologists would focus on for years to come. Crucially, the approach of Wundt and James did not involve metaphysics or religious explanations of human thought and behaviour, freeing it from the realms of philosophy and theology, and in many people's eyes, founding the modern science of psychology.

Meanwhile, Sigmund Freud had invented and applied a method of psychotherapy known as psychoanalysis. Freud's understanding of the mind was largely based on interpretive methods and introspection (a technique also championed by Wundt), but was particularly focused on resolving mental distress and psychopathology. Freud's theories were wildly successful, not least because they aimed to be of practical benefit to individual patients, but also because they tackled subjects such as sexuality and repression as general aspects of psychological development. These were largely considered taboo subjects at the time, and Freud provided a catalyst for them to be openly discussed in polite society. Although it has become fashionable to discredit many of Freud's more outlandish theories, his application of psychology to clinical work and his more mainstream work has been massively influential.

Partly as a reaction to the subjective and introspective nature of psychology at the time, behaviourism began to become popular as a guiding psychological theory. Championed by psychologists such as John B. Watson, Edward Thorndike and B. F. Skinner it argued that psychology should be a science of behaviour, not the mind, and rejected the idea of internal mental states such as beliefs, desires or goals, believing all behaviour and learning to be a reaction to the environment. In his classic 1913 paper Psychology as the behaviourist views it Watson argued that psychology "is a purely objective experimental branch of natural science", "introspection forms no essential part of its methods..." and "The behaviourist... recognizes no dividing line between man and brute".

Behaviourism was the dominant model in psychology for much of the early 20th century, largely due to the creation and successful application (not least of which in advertising) of conditioning theories as scientific models of human behaviour.

However, it became increasingly clear that although behaviourism had made some important discoveries, it was deficient as a guiding theory of human behaviour. Noam Chomsky's review of Skinner's book Verbal Behaviour (that aimed to explain language acquisition in a behaviourist framework) is considered one of the major factors in the ending of behaviourism's reign. Chomsky demonstrated that language could not purely be learnt from conditioning, as people could produce sentences unique in structure and meaning that couldn't possibly be generated solely through experience of natural language, implying that there must be internal states of mind that behaviourism rejected as illusory. Similarly, work by Albert Bandura showed that children could learn by social observation, without any change in overt behaviour, and so must be accounted for by internal representations.

The rise of computer technology also promoted the metaphor of mental function as information processing. This, combined with a scientific approach to studying the mind, as well as a belief in internal mental states, led to the rise of cognitivism as the dominant model of the mind.

Links between brain and nervous system function were also becoming common, partly due to the experimental work of people like Charles Sherrington and Donald Hebb, and partly due to studies of people with brain injury (see cognitive neuropsychology). With the development of technologies for accurately measuring brain function, neuropsychology and cognitive neuroscience have become some of the most active areas in contemporary psychology.

With the increasing involvement of other disciplines (such as philosophy, computer science and neuroscience) in the quest to understand the mind, the umbrella discipline of cognitive science has been created as a means of focusing such efforts in a constructive way.

However, not all psychologists have been happy with what they perceive as 'mechanical' models of the mind and human nature.

Carl Jung, a one-time follower and contemporary of Freud, was instrumental in introducing notions of spirituality into Freudian psychoanalysis (Freud had rejected religion as a mass delusion).

Humanistic psychology emerged in the 1950s and has continued as a reaction to positivist and scientific approaches to the mind. It stresses a phenomenological view of human experience and seeks to understand human beings and their behaviour by conducting qualitative research. The humanistic approach has its roots in existentialist and phenomenological philosophy and many humanist psychologists completely reject a scientific approach, arguing that trying to turn human experience into measurements strips it of all meaning and relevance to lived existence.

Some of the founding theorists behind this school of thought are Abraham Maslow who formulated a hierarchy of human needs, Carl Rogers who created and developed client centred therapy, and Fritz Perls who helped create and develop Gestalt therapy.

Major nineteenth and twentieth century schools of thought
Various schools of thought have argued for a particular model to be used as a guiding theory by which all, or the majority, of human behaviour can be explained. The popularity of these has waxed and waned over time. Some psychologists may think of themselves as adherents to a particular school of thought and reject the others, although most consider each as an approach to understanding the mind, and not necessarily as mutually exclusive theories.

behaviourism (see also radical behaviourism)
cognitivism
functionalism
Gestalt psychology
humanistic psychology and phenomenology
psychoanalysis
structuralism

Modern psychology
The majority of mainstream psychology is based on a framework derived from cognitive psychology, although the popularity of this paradigm does not exclude others, which are often applied as necessary. Alternatively, a psychologist may specialise in an area in which cognitive psychology is rarely used.

A psychologist will often attempt to measure or test different aspects of psychological function, using psychometric and statistical methods, including well known standardised tests as well as those created as the situation requires.

Academic psychologists may focus purely on research, aiming to further psychological understanding in a particular area, while other psychologists may work in applied psychology to deploy such knowledge for immediate and practical benefit. However, these approaches are not mutually exclusive and most psychologists will be involved in both researching and applying psychology at some point during their work.

Contemporary psychology is broad-based and consists of a diverse set of approaches, subject areas and applications. A comprehensive list is given in the Topics and Divisions sections below. Where an area of interest is considered to need specific training and specialist knowledge (especially in applied areas), psychological societies will typically set up a governing body to manage training requirements. Similarly, requirements may be laid down for university degrees in psychology, so that students acquire an adequate knowledge in a number of areas. While the exact divisions may vary from country to country, the following areas are usually considered as 'core' subjects or approaches by psychology societies and universities.

Cognitive psychology
Cognitive psychology is a framework in which to understand the mind more than a subject area, although it has traditionally focused on certain aspects of psychology. Perception, learning, problem solving, memory, attention, language and emotion are all well researched areas. Cognitive psychology is based on a school of thought known as cognitivism, which argues for an information processing model of mental function, informed by positivism and experimental psychology. Techniques and models from cognitive psychology are widely applied and form the mainstay of psychological theories in many areas of both research and applied psychology.

Clinical and counselling psychology
Clinical psychology is the application of psychology to the understanding, treatment and assessment of psychopathology, behavioural or mental health issues. It has traditionally been associated with counselling and psychotherapy, although modern clinical psychology may take an eclectic approach, including a number of therapeutic approaches. Typically, although working with many of the same clients as psychiatrists, clinical psychologists do not prescribe psychiatric drugs. Clinical psychologists largely work within the 'scientist-practictioner model' where clinical problems are formulated as hypotheses to be tested as information is gathered about the patient and their mental state. Some clinical psychologists may focus on the clinical management of patients with brain injury. This is known as clinical neuropsychology and typically involves additional training in brain function.

In recent years and particularly in the United States, a major split has been developing between academic research psychologists in universities and some branches of clinical psychology. Many academic psychologists believe that these clinicians use therapies based on discredited theories and unsupported by empirical evidence of their effectiveness. From the other side, these clinicians believe that the academics are ignoring their experience in dealing with actual patients. The disagreement has resulted in the formation of the American Psychological Society by the research psychologists as a new body distinct from the American Psychological Association.

Developmental and educational psychology
Largely focusing on the development of the human mind through childhood (although development through adulthood is also studied), developmental psychology seeks to understand how children come to perceive, understand and act within the world. This may focus on intellectual, cognitive, neural, social or moral development and involve a number of unique research methods to engage children in experimental tasks. These tasks often resemble specially designed games and activities that are both enjoyable for the child and scientifically useful. Educational psychology largely seeks to apply much of this knowledge and understand how learning can best take place in educational situations. Because of this, the work of child psychologists such as Lev Vygotsky, Jean Piaget and Jerome Bruner has been influential in creating teaching methods and educational practices.

Forensic psychology
Forensic psychology is concerned with the psychology of crime, criminals and law enforcement. A forensic psychologist may be involved in assessment of offenders or interventions to prevent offending behaviour, usually with people who have already come in contact with the legal or penal system. Often this involves working with offenders with mental health problems, or with people who act dangerously or in an antisocial manner (for example, psychopaths). Criminal profiling is another important role fulfilled by forensic psychologists and typically involves building psychological profiles of unknown or at-large offenders from the known evidence.

Health psychology
While clinical psychology focuses on mental health and neurological illness, health psychology is concerned with the psychology of a much wider range of health related behaviour. For example, healthy eating, the doctor-patient relationship, a patient's understanding of health information and beliefs about illness. Health psychologists may be involved in public health campaigns, examining the impact of illness or health policy on quality of life or research into the psychological impact of health and social care.

Industrial and organisational psychology
Involved with the application of psychology to the world of business, commerce and the function of organisations, industrial and organisational psychology focuses to varying degrees on the psychology of the workforce, customer and consumer, including issues such as the psychology of recruitment, training, appraisal, job satisfaction, stress at work and management. Psychologists may also work on product design, interaction with machines or software, advertising, sales and marketing, to aid functionality, safety and appeal.

Neuropsychology
Neuropsychology is a branch of psychology that aims to understand how the structure and function of the brain relates to specific psychological processes. Often neuropsychologists are employed as scientists to advance scientific or medical knowledge. Cognitive neuropsychology is particularly concerned with the understanding of brain injury in an attempt to work out normal psychological function. Clinical neuropsychology is the application of neuropsychology for the clinical management of patients with neurocognitive deficits.

Social psychology
Social psychology aims to understand how the mind makes sense of social situations. For example, this could involve the influence of others on an individual's behaviour (e.g. conformity or persuasion), the perception and understanding of social cues, or the formation of attitudes or stereotypes about other people. Social cognition is a common approach and involves a mostly cognitive and scientific approach to understanding social behaviour.

Topics in psychology
Although in principle, psychology aims to explain all aspects of thought and behaviour, some topics have generated particular interest, either due to their perceived importance, their ease of study or popularity. Many of the concepts studied by professional psychology stem from the day-to-day psychology used by most people and learnt through experience. This is known as folk psychology to distinguish it from psychological knowledge developed through formal study and investigation. The extent to which folk psychology should be used as a basis for understanding human experience is controversial, although theories that are based on everyday notions of the mind have been among some of the most successful.

For a comprehensive list of psychological topics on wikipedia, please see the list of psychological topics.

addiction
anti-social behaviour
attention
attitude
brain and nervous system function
brain injury
child development
cognition
communication
conditioning
conformity
consciousness
crime
decision making
emotion
ergonomics
executive function
experimental analysis of behaviour
face perception
group dynamics
human computer interaction
language and language acquisition
learning
memory
mental illness
motivation
perception
personality
problem solving
program evaluation
psychological testing
psychopathology
psychopharmacology
psychotherapy
reasoning and decision making
rehabilitation
reinforcement
research methods
sensory experience
sexuality and gender role
social cognition
social influence
vision

Divisions and approaches in psychology
Different disciplines in psychology typically signify both a set of practices and an area of interest. The divisions are largely arbitrary and overlapping (although they may have been formalised into areas of interest by psychological societies or regulatory bodies) and most psychologists will use methods from each area as appropriate, even if they mostly focus on one area of interest in their work.

abnormal psychology
analytical psychology
applied psychology
behavioural medicine
behavioural psychology
biobehavioural health
biological psychology
cognitive neuropsychology
cognitive psychology
cognitive neuroscience
community psychology
comparative psychology
clinical psychology
counselling psychology
critical psychology
developmental psychology
educational psychology
emotional clearing
evolutionary psychology
experimental psychology
forensic psychology
health psychology
humanistic psychology
individual differences psychology
industrial and organisational psychology
medicinal psychology
medical psychology
neuropsychology
personality psychology
physiological psychology
popular psychology, self-help, and alternative therapy
positive psychology
pre- and perinatal psychology
problem solving
psychoanalysis
psychohistory
psychometrics
psychonomics
psychophysics
psychophysiology
psychotherapy a branch of psychiatry as well
social psychology
traffic psychology
transpersonal psychology

Some related disciplines
artificial consciousness (see also simulated consciousness)
cognitive science
complex systems
computer science and captology
economics and marketing
ethology
game theory
history
hypnotherapy
linguistics and especially psycholinguistics
literature, literary theory, and critical theory
neuroeconomics
neuro-linguistic programming
neuroscience
parapsychology
philosophy of mind
philosophy of psychology
psychometrics
psychophysics
sociology
socionics
systems theory

Psychology Resources
AmoebaWeb Psychology Resources (http://www.vanguard.edu/faculty/ddegelman/amoebaweb/)
A Century of Psychology (APA) (http://www.apa.org/monitor/dec99/toc.html)
Classics in the History of Psychology (http://psychclassics.yorku.ca)
Dictionary of Psychology (http://allpsych.com/dictionary/)
Encyclopedia of Psychology (http://www.psychology.org/)
New Scientist news on the mind (http://www.newscientist.com/hottopics/humannature/sectindex.jsp?sub=The%20mind) and brain (http://www.newscientist.com/hottopics/humannature/sectindex.jsp?sub=The%20brain)
Pictures of famous psychologists (http://www.sonoma.edu/psychology/psychart.html)
Psychology Conferences (http://www.conferencealerts.com/psychology.htm)
Psychology Congresses (http://www.perfectionnement.info/lo/agenda.php?i_pays=0&i_date=0&keywords=congr)
ScienceDaily Mind and Brain news (http://www.sciencedaily.com/news/mind_brain.htm)

Psychology Societies
American Psychological Association (http://www.apa.org)
American Psychological Society (http://www.psychologicalscience.org/)
British Psychological Society (http://www.bps.org.uk)
Canadian Psychological Association (http://www.cpa.ca)