Here are three key works by Sigmund Freud which, published in the first decades of the 20th century, underpinned his developing views and had such a dramatic effect on world society. In the uncompromising Three Essays on the Theory of Sexuality (1905), he declared that 'sexual aberrations' are not limited to the insane but exist in 'normal' people to a greater or lesser degree. The three essays are divided between sexual perversions, childhood sexuality and puberty.

This series of 28 lectures was given by Sigmund Freud (1856-1939), the founder of psychoanalysis, during the First World War and first published in English in 1920. The purpose of this general introduction was to present his work and ideas - as they had matured at that point - to a general public; and even though there was to be considerable development and change over the ensuing years, these talks still offer a valuable and remarkably approachable entry point to his revolutionary concepts.

In this 1912 work, Jung seeks to find symbolic meaning and purpose behind a given set of symptoms within the larger context of the psyche. It examines the fantasies of a patient whose vivid and poetic mental images enabled Jung to redefine libido as psychic energy which arises from the unconscious to manifest itself consciously in symbolic form. The work marks a theoretical divergence between Jung and Freud on the nature of the libido. 

Modern Man in Search of a Soul is the classic introduction to the thought of Carl Jung. Along with Freud and Adler, Jung was one of the chief founders of modern psychiatry. In this book, Jung examines some of the most contested and crucial areas in the field of analytical psychology: dream analysis, the primitive unconscious, and the relationship between psychology and religion.

What are the most common dreams and why do we have them? What does a dream about death mean? What do dreams of swimming, failing, or flying symbolize? First published by Sigmund Freud in 1899, The Interpretation of Dreams considers why we dream and what it means in the larger picture of our psychological lives.