The Spacing Guild, also known as the Guild of Navigators, or more simply the Guild, was an organization which held exclusive access to faster than light space travel. The Guild monopoly on space travel and transport and upon interstellar banking is taken as the beginning point of the Imperial Calendar.
Around the Time of the Great Convention
After the Bene Gesserit, the Spacing Guild was the second mental-physical training school established following the Butlerian Jihad. The genesis of the Guild's eventual monopoly on space travel, transport and interstellar banking is taken as the beginning point of the Imperial Calendar. Details of the Guild's emergence are contentious, although it is believed they emerged as a serious political and economic force around the time of The Great Convention.
During the Corrino Empire
While the exact evolution of the Guild's monopoly on faster-than-light space travel is not given, they do nonetheless wield this formidable power throughout the history of the Corrino Empire, a time known as the Guild Peace. Paul Atreides was the first emperor to check the power of the guild through control of the spice melange, although they remained a significant political power.
Impact of the God-Emperor
New problems for the Spacing Guild were created by the ascendancy of Leto Atreides II to the title of God Emperor. Leto's extremely long lifespan, coupled with his decision to realize the Golden Path strategy, saw him hoard the Spice Melange with no concern for short-term problems.
Thus, over the many centuries of his rule, the Spacing Guild was forced to do his bidding and their unique powerbase of old was significantly diminished.
While the Spacing Guild remained a powerful body even after the death of Leto Atreides II, their power gradually eroded over time. By the time of the arrival of the Honored Matres the success of the groups sent out in the Scattering had created new but largely unknown threats to their hegemony. This was because Ixian no-ships, which could perform the same functions of a Guild Navigator, were in common use. As a result, the Guild no longer had a monopoly on space travel.
The Spacing Guild was by its very nature a secretive organization that took up functions previously covered by the Thinking Machines, just as mentats and the Bene Gesserit did. Their very existence rests on the proprietary knowledge they had clung to for thousands of years.
The inner structure of the Guild during and after the time of Paul Atreides was never fully revealed. However, it is known that the role of Guild Navigator was most prestigious, and the ambition of almost all of those who joined the Guild.
Other known Guild roles included the Chief Administrator, the administrative staff, Navigator attendants, Guild ambassadors, and technical support staff. Members of the Guild commonly wear gray uniforms with the Guild's analemma sigil of infinity emblazoned on the sleeves.
The Guild Navigators were utterly dependent on the Spice Melange to safely deliver a vessel via the Holtzman Effect. Even a partial restriction on the Guild's spice requirements rendered them powerless, and reduced long distance trade and transport to a snail's pace.
Prior to the discovery of the Spice Melange's prescient powers, the use of the Spacefolder was very dangerous. One in about every eight Spacefolders was destroyed during travel, because of the lack of a viable method for avoiding gravitational hazards.