The word "modern" in this context is generally assumed to cover the period from about 1880 to the present day, or from the roots of modernism to the present day, but this has been a matter of debate for many years.

Whilst exactly the same principles apply as to books printed before the age of the machine, certain special considerations arise. [from Gaskell:] Many twentieth-century books have a statement on the verso of the title-page recording the date of the first edition and subsequent editions and impressions. On more recent books impressions are often distinguished by an ascending, descending or counterbalancing sequence of numbers on the verso of the title-leaf, generally beginning or ending in the number of the impression. At each subsequent reprinting one digit is omitted, so to identify the ‘first impression’ it is important to note that the sequence begins with, ends with, or includes a figure 1 (or its equivalent): this indicates the first impression - the only one that may be called a first edition without further qualification. [end of Gaskell]. However, this is only one example (albeit the most common) of a welter of different numbering and lettering systems used. Several guides have been issued to assist with this problem.

Unless otherwise stated, where a dustwrapper is present it should be the one in which that particular copy of the book was originally issued.

The existence of digital media may cause some confusion and apparently create grey areas, but the underlying principle of chronological precedence applies.

Dustwrappers (or dust-jackets) themselves sometimes have various impressions or states, which may or may not correspond with different issues of the book. A first impression of a book in a supplied dustwrapper will be greatly devalued if current (or indeed subsequent/future) research shows the wrapper to have been supplied from a later impression or state. The condition of the book should be examined to make sure it is consistent with the condition, or indeed presence, of the dustwrapper, and unless a coherent explanation is given, any discrepancy should be viewed with suspicion.
(December 2005)

ABA members must mark all facsimile dustwrappers indelibly and that marking must be clearly visible in normal light. Facsimile dust-wrappers may not be exhibited at ABA book fairs.
(April 2006)