Carl Gustav Jung was born in1875 in a small Swiss village of Kessewil. His father was a country parson, as were other relatives. Jung began studying classics at a very early age (as young as six), and became an expert in ancient languages and literature, including Latin, Greek, Hebrew and Sanskrit. His first academic choice was archaeology, but instead studied medicine at the University of Basel. While working under famed neurologist Krafft-Ebing, he decided upon psychiatry. He worked with schizophrenics, and is also the inventor of the word-association process in therapy. He had a long-time admiration of Freud, one of the founders of his field, and met him in 1907 (in what was reported to have been a 13-hour long conversation!). A close association followed, but only for a few years, as Jung's ideas began to vary somewhat with Freud, and Freud's occasional paranoia crept into the relationship. After 1909, they were distant.
Jung was a visionary, in more ways than one. In 1913 he thought he was having psychotic episodes by having dreams and visions of blood-filled rivers, endless winters and mass death. Jung's sense of the power of the collective unconscious comes partly from experiences such as this, for in 1914 the first world war began, and his visions seemed to have a prophetic ring to them.
After the war, Jung took an active interest both in developing his ideas as well as travelling and learning around the world from people in different settings -- this included people in indigenous cultures in Africa, the Americas and India. He was active in the field until the mid-1950s; he died in 1961.
Jung worked with Freudian ideas, but did not adopt Freud's framework without significant modifications (and there were parts he outright rejected). Jung saw the interior structure in a tripartite set-up -- the ego, the personal unconscious, and the collective unconscious. The collective unconscious is not the superego of Freudian theory, but rather a typse of psychic inheritance, a species-level knowledge that possibly even extends into the future (like his visions).
Another primary development of Jung is the idea of archetypes -- given his literary and linguistic background, this would seem to be a natural for Jung. These are mythical or primordial images -- much of religious literature is full of them; legends exemplify them. Archetypes can be easily understood (such as the mother archetype, the hero archetype) or more obscure (the anima and animus, the mana, the shadow).
This volume of Jung's work is compiled and introduced by none other than Joseph Campbell ('The Power of the Myth'), who worked so closely with the Star Wars group to turn it into a modern legend, full of Jungian-style archetypes. Jung's work spans much of spirituality, psychiatry/psychology, and even gets into political and philosophical territory. Campbell gives a good selection of Jung's works here, intending it to be both an introduction to Jung's psychological theories as well as his love for and realisation of the importance of mythology and religious lore of all people.
The first section has eight essays or selections that deal with particular psychological theory pieces -- the structure of the psyche, the stages of life, psychological types (the precursor of Myers-Briggs and other types of psychological type assessments). The second section deals with more 'spiritual' topics and dream analysis -- the relationship of psychology to poetry, the spiritual problem of the moderns, etc. The third section contains two essays -- On Synchronicity, a lecture he gave dealing with such things as deja vu and coincidence, and his 'Answer to Job', tackling the very tricky subject of the nature of God in the Hebrew scriptures in an interesting manner.
Campbell gives some additional reading suggestions in the appendix, divided by topic. Of course, one might pick up Campbell's own books as well.