Introduced by Adobe in 1985, the page description language known as PostScript has undergone improvements and changes over the years. Just as new versions of software contain new features not available in earlier versions, subsequent PostScript levels have added support for new features and the way the underlying code is written has undergone modifications. 

The key differences in the primary PostScript levels are:

1. Adobe PostScript Level 1 was the original, basic language.
2. Adobe PostScript Level 2 added support for different page sizes and better color printing.
3. Adobe PostScript Level 3, released in 1997, has better graphics handling, supports more fonts, and speeds up printing.

In terms of desktop publishing, the PostScript level used for creating PostScript (and PDF) files is partially dependent on the PostScript levels supported by the printer and the printer driver. Older printer drivers and printers cannot interpret some of the features found in PostScript Level 3, for example.