Bookmarked "Harry Houdini Collection (Library of Congress) DLC" (archive.org)
Harry Houdini (1874-1926), master magician and escape artist, wrote in A Magician Among the Sprits, (1924) that he had "accumulated one of the largest libraries in the world on psychic phenomena, Spiritualism, magic, witchcraft, demonology, evil spirits, etc., some of the material going back as far as 1489." In 1927, through Houdini's bequest, the Library received 3,988 volumes from his collection. While strongest in nineteenth and twentieth century publications on spiritualism- Houdini doubted "if any one in the world has so complete a library on modern Spiritualism: - the Houdini Collection contains a number of magic books inscribed or annotated by well-known magicians. Leonard N. Beck. discusses significant items in "Things Magical in the Collections of the Rare Book Division," QJLC, v. 31, October 1974, p. 208-234. Also in the collection are prints, playbills, printed ephemera, periodicals, and many volumes of pamphlets on such topics as card tricks, mediums, hypnotism, handcuff escape methods, and chalk-talking. Of special note are over one hundred unannotated scrapbooks containing theatre notices and news clippings on subjects of personal interest. Houdini's theatrical collection was sold after his death to Messmore Kendall and later donated to the University of Texas.
A cool collection I ran across the other day.

👓 Most valuable book ever. | The Magic Cafe Forums

Read Most valuable book ever. by jamessmithjamessmith (The Magic Cafe Forums - themagiccafe.com)
This is a very old thread that Delimbeau has re-opened and I think that the answer is extremely subjective. It depends how you define "value"; whether it be in respect of content or monetary worth. If the former, there are probably as many answers as there are books but if - as I think was the original ask - it is purely monetary there are only a few candidates, most of which have already been mentioned. First let's ditch Scot's "Discoverie of Witchcraft". Whilst the second issue of the third edition is likely the scarcest, the first edition will almost always be more valuable. Aside the magic content, this is a very desirable book in many fields and therefore always commands high prices. It is not, however, rare. As an update on price, copies of the first edition in the last couple of years have reached up to c. $70,000. Compare this with the aforementioned third edition, a copy of which a couple of weeks ago sold for "only" $14,000 + commission (in itself a high price). The Guyot, Dean and Pinetti mentioned in the thread we can also discount, as "comparatively" they are of little value (in any edition). Of known books on magic, likely "The Art of Jugling" (1st ed. 1612, 2nd ed. 1614) or "Hocus Pocus Junior" (1st ed. 1634, 2nd. ed 1635) would be the most valuable. "The Art of Jugling" was the first book solely devoted to magic in the English language (albeit plagiarised from Scot) and only one copy has been offered for sale in the lifetime of most people who will read this. The six-figure dollar asking price would exceed any copies of Scot's work I know of. Of course, "asking" and "sale" price will not necessarily be the same. Recent (i.e. last 10 years or so) copies of "Hocus Pocus Junior" have "only" reached the c. $36,000-$60,000 price range. These have been later editions. That said, a first edition certainly would achieve a price well above that, if one were to emerge - unlikely since none has been seen since the 1930s. In the event that it did, it may well exceed those prices recently realised by Scot first editions. Probably the most valuable book on magic is one that we do not yet know exists, or suspect that it does but a copy has never been seen. For example, some may be aware of Prevost's "La Premiere partie des subtiles et plaisantes inventions". It is a French illustrated book devoted solely to magic that predates Scot (by only a few months). As it is not in English it doesn't get as much attention but is arguably much more exciting from a purely magical context. For those French readers, you will note that Prevost's book was the "first part" (i.e. premiere partie). If a second part were to emerge, I would warrant it very valuable indeed. The potential "second part" of Prevost is but one example. Lost manuscripts or other early works (most likely in Italian) may also compete. The fact is, though, that regardless of content the majority of the market is English speaking, so early English works are likely to continue to command the highest prices, regardless of their rarity or importance. We must also remember that our field of interest is very niche. Another book with magic in it but with much wider appeal would attract more attention and - potentially - command a higher price; i.e. the high prices seen recently for first edition Scot's are predominantly NOT due to magic collectors but collectors with other fields of interest.

🔖 La Première partie des subtiles et plaisantes inventions, comprenant plusieurs jeux de récréation et traicts de soupplesse, par le discours desquels les impostures des bateleurs sont descouvertes. par Jean Prévost | Gallica

Bookmarked La Première partie des subtiles et plaisantes inventions, comprenant plusieurs jeux de récréation et traicts de soupplesse, par le discours desquels les impostures des bateleurs sont descouvertes. by Jean Prévost (Gallica)
The earliest known important book on conjuring or magic, printed in French in Lyons in 1584.
hat tip: Ricky Jay’s Magical Secrets (The New Yorker)

👓 Ricky Jay’s Magical Secrets | The New Yorker

Read Ricky Jay’s Magical Secrets (The New Yorker)
Jay’s deft illusions flout reality, and he rejects the notion that his magic is a suitable entertainment for children.
A great set of stories about Ricky Jay.

Highlights, Quotes, Annotations, & Marginalia

I once asked Mamet whether Jay had ever shared with him details of his childhood.Mamet replied, “I can’t remember.”I said, “You can’t remember whether you discussed it or you can’t remember the details?”He said, “I can’t remember whether or not I know a better way to dissuade you from your reiteration of that question without seeming impolite.”  

November 29, 2018 at 12:44PM

Magic is about working hard to discover a secret and making something out of it. You start with some small principle and you build a theatrical presentation out of it. You do something that’s technically artistic that creates a small drama.  

November 29, 2018 at 12:48PM

Jean Prévost’s “La Première Partie des Subtiles et Plaisantes Inventions,” the earliest known important conjuring book, printed in Lyons in 1584.  

November 29, 2018 at 01:15PM

The main thing that dissuaded him, he says, is that “I wouldn’t want to sell a book to a philistine, which is what every bookseller has to do.”  

November 29, 2018 at 01:18PM

Two automatons stood on the table. One, called “The Singing Lesson,” was the creation of Jean-Eugène Robert-Houdin, the nineteenth-century watchmaker-turned-conjurer, who is considered the father of modern magic. The other was a Chinese cups-and-balls conjurer built by Robert-Houdin’s father-in-law, Jacques Houdin.  

November 29, 2018 at 01:34PM

Two automatons stood on the table. One, called “The Singing Lesson,” was the creation of Jean-Eugène Robert-Houdin, the nineteenth-century watchmaker-turned-conjurer, who is considered the father of modern magic. The other was a Chinese cups-and-balls conjurer built by Robert-Houdin’s father-in-law, Jacques Houdin.  

November 29, 2018 at 01:34PM

📺 Ricky Jay – 4 Queens 3 Ways | YouTube

Watched Ricky Jay: 4 Queens 3 Ways from YouTube

The incomparable Mr Jay demonstrating differing styles of patter and presentation working around a theme of the Four Ladies

The language here is almost more complicated than the trick.

📺 Ricky Jay – Late Night with Conan O’Brien (September 25, 2002) | YouTube

Watched Ricky Jay - Late Night with Conan O'Brien (September 25, 2002) from YouTube

Master close-up magician and historian Ricky Jay makes an extremely rare television appearance on Conan O'Brien's show in 2002 and performs several effects.

👓 Ricky Jay, Magician and 'Boogie Nights' Actor, Dies at 72 | New York Times

Read Ricky Jay, Magician and 'Boogie Nights' Actor, Dies at 72 (The Hollywood Reporter)
In addition to his long career as a magician, he also appeared in such films as 'Magnolia' (1999) as the narrator, 'Tomorrow Never Dies' (1997) as a cyber terrorist and 'Boogie Nights' (1997).
I had friends who represented Rick Jay when I was at CAA. I later had the privilege of working with him as a consultant on Heartbreakers, when he had me out to the Magic Castle several times as a guest.

I don’t think there’s anyone living or dead who had a better collection or mastery of magic and related arts than Ricky Jay did. I hope his legacy and library is well supported.