The Interpretation of Dreams (1899) is one of Sigmund Freud's most notable works. Some of Freud's most important ideas such as the unconscious and the Oedipal complex are manifested in the book which makes it pivotal in any understanding of Sigmund Freud's theory or psychoanalysis in general.
As suggested by its title, The Interpretation of Dreams is primarily devoted to the study of dreams and their role in mental life and therapy. Freud argues that all dreams are subjected to the need for "wish fulfillment" (wunscherfüllung), a notion he will later renounce (see Beyond the Pleasure Principle) but at the time was fundamental to his theory. Dreams, Freud held, are an instrument to maintain sleep and in order to do so must cater for different needs arising in the body and psyche during sleep. In order to prevent these needs from waking us up the mind sets up imagined experiences that offer relief and satisfaction for these urges. Dreams can, for example, hold off the need for peeing by giving you a dream in which you are relived. In a more complex example the dream offers some resolve to a haunting inner conflict by enacting its desired outcomes.
The thing about wish fulfillment is that we don't always want to know what our true wishes are (especially if you take the Freudian view on humans and their objects of desire). This is where the "censor" comes in, blurring the content of the dream and rendering it incomprehensible so that we are not exposed to anything we don't want to acknowledge. In order for information to slip through the censor lines it must be coded. This means that dreams, much like in the biblical or mystic notion of them, have deep symbolic meaning to them.
In The Interpretation of Dreams Freud termed the concept of Dreamwork in order to refer to the mechanisms that take part in the symbolic formation of the dream. Dreamwork includes, as a start, symbolism and the fact the different psychic entities in our soul receive visual representation in the dream. Freud also notes two types of such symbolic mechanism such as displacement which combines two meanings into one object or displacement which moves feeling directed at one object to another. In the end comes what Freud calls secondary revision, the "editing" of the dream by the dreamer in order to apply logic and coherence to it.
In psychoanalysis the dream serves, according to Freud, as "the royal road to the unconscious". The dream provides the therapist with data which is usually not obtainable by the conscious awake self, and by deconstructing its coded meanings one can get a peak at what's happening deep down under.
Although Freud later retracted many of the ideas that appear in The Interpretation of Dreams, the book remains highly influential till this days, maybe because it contains some spectacular demonstrations of dream analysis conducted by Freud that are sure to leave you waiting for next morning.
Other articles and summaries about Freud:
Sigmund Freud - Totem and Taboo
Books of interest: