Samuel Chiltern answered
The major trends in the development of psychology can be divided into five main schools of thought, which I'll outline briefly in the rest of this answer.
Structuralism
Psychology began to split from biology towards the end of the 19th century.
Edward Titchener, a student of Wilhem Wundt, set up the first psychological school of thought, drawing upon the work of Wundt, and combining it with his own research and ideas.
The aim of structuralism was to break down mental processes into the smallest possible units, using a scientifically-discredited technique known as introspection.
The key criticism of this approach is that, although it attempts to adhere to scientific rigour, it still relies upon a person's own perception of their mental processes, which is not scientifically valid.
Psychoanalysis
This is probably the most famous of all psychological schools of thought, mainly due to the work of Sigmund Freud, who founded it in 1916-1917.
Psychoanalysis was based on techniques similar to introspection, and focused on relieving distress in patients by helping them to uncover repressed emotions and experiences. There was no scientific basis to Freud's work, and it has since been largely discredited in scientific circles.
Behaviourism
Behaviourism eventually replaced structuralism in the 1950s as the purely scientific branch of psychology. It used direct observation, instead of the personal accounts of the subject, to understand learning processes. It focused on how reward can be used to condition behaviour in animals and humans.
Humanistic Psychology
Sometimes referred to as positive psychology, humanistic psychology focuses on helping people to develop their skills and abilities. It focuses on what people can do, rather than giving too much attention to their abnormalities, and treats patients by helping them to develop emotional and interpersonal skills, amongst others.
Cognitive Psychology
Cognitive psychology interlinks with neuroscience and linguistics, and is concerned with how an individual's perceptions and experiences can be measured objectively. Practitioners might do this, for example, by using brain scanning technology to observe a patient whilst they recount a distressing memory, or think about certain words.
Structuralism
Psychology began to split from biology towards the end of the 19th century.
Edward Titchener, a student of Wilhem Wundt, set up the first psychological school of thought, drawing upon the work of Wundt, and combining it with his own research and ideas.
The aim of structuralism was to break down mental processes into the smallest possible units, using a scientifically-discredited technique known as introspection.
The key criticism of this approach is that, although it attempts to adhere to scientific rigour, it still relies upon a person's own perception of their mental processes, which is not scientifically valid.
Psychoanalysis
This is probably the most famous of all psychological schools of thought, mainly due to the work of Sigmund Freud, who founded it in 1916-1917.
Psychoanalysis was based on techniques similar to introspection, and focused on relieving distress in patients by helping them to uncover repressed emotions and experiences. There was no scientific basis to Freud's work, and it has since been largely discredited in scientific circles.
Behaviourism
Behaviourism eventually replaced structuralism in the 1950s as the purely scientific branch of psychology. It used direct observation, instead of the personal accounts of the subject, to understand learning processes. It focused on how reward can be used to condition behaviour in animals and humans.
Humanistic Psychology
Sometimes referred to as positive psychology, humanistic psychology focuses on helping people to develop their skills and abilities. It focuses on what people can do, rather than giving too much attention to their abnormalities, and treats patients by helping them to develop emotional and interpersonal skills, amongst others.
Cognitive Psychology
Cognitive psychology interlinks with neuroscience and linguistics, and is concerned with how an individual's perceptions and experiences can be measured objectively. Practitioners might do this, for example, by using brain scanning technology to observe a patient whilst they recount a distressing memory, or think about certain words.
