It is said to have supplanted the rival Encyclopedia Galactica as a "standard repository of all knowledge and wisdom" in some parts of the galaxy for two reasons, one of them being that has a slightly cheaper price, and the other that it has the words "DON'T PANIC" printed on its cover.

As well as offering background information, the Guide's entries often employ irony, sarcasm and subtle commentary on the action and on life in general.

For instance, the entry on the Sirius Cybernetics Corporation describes their marketing division as "a bunch of mindless jerks who will be the first against the wall when the revolution comes", with a footnote to the effect that the editors would welcome applications from anyone interested in taking over the post of robotics correspondent.

"[4] The entry on "What to do if you find yourself stuck in a crack in the ground underneath a giant boulder you can't move, with no hope of rescue" suggests that first, you "consider how lucky you are that life has been good to you so far.

"[9] Despite the work of dedicated field researchers such as Ford Prefect, many of the contributions to the Guide are made on a strictly ad-hoc basis.

"[10] This has led to the Guide being patchy in its coverage, cobbled together (for example: the entry on "The Universe" was copied from the back of a packet of breakfast cereal)[11] and often riddled with errors.

The novel of the same name notes that "it has many omissions and contains much that is apocryphal, or at least wildly inaccurate ...." Although Ford puts together a lengthy and detailed entry on Earth during the 15 years he is stranded there, the editors cut it down to two words: "Mostly harmless."

In So Long, and Thanks for All the Fish, he is stunned to see his entire original work restored during a database update, even though he saw the planet being demolished by the Vogons.

The change turns out to be necessary because another Earth has been pulled into existence from a parallel universe by dolphins in order to prevent humans from becoming extinct.

In the first book, Ford's copy of the Guide is described as looking "rather like a largish electronic calculator" and "insanely complicated", with "about a hundred tiny flat press buttons and a screen about four inches square" which could display any of a million pages.

In So Long, and Thanks for All the Fish, Arthur's copy is described as resembling "a small, thin, flexible lap computer" encased in a "sturdy plastic cover" with the words "Don't Panic" inscribed on it "in large, friendly letters".

[14] Arthur's copy of the Guide is described as "battered and travelworn" by this point in the series, having survived being thrown into a river, "frozen on the glaciers of the moon of Jaglan Beta, sat on, kicked around spaceships, scuffed and generally abused".

This Guide, which takes the form of a black, birdlike robot, appears pleasant and friendly but is in fact deeply malevolent and in league with the Vogons in a plot to destroy Earth.

Strangely enough, it saves all the main characters from certain doom as part of some unknown agenda and disappears from existence shortly before the Grebulons destroy Earth at the beginning of the sixth book in the series, And Another Thing by Eoin Colfer.

In the television series, Jones's voice was left unfiltered for both the Guide and "general" narrations, which were accompanied by hand-drawn animations representing computer readouts.

These animations often contained little jokes, such as the full text of the "worst poetry in the universe", the equation of 37 Earth miles as "1 Altairian long way", the inclusion of a topping of meringue on a Magrathea-constructed planet, and the outcome of an intergalactic war represented as a video game score.