The previous version of LaTeX was known as LaTeX 2.09. Over the years many extensions have been developed for LaTeX. This is, of course, a sure sign of its continuing popularity but it has had one unfortunate result: incompatible LaTeX formats came into use at different sites. This included `standard LaTeX 2.09', LaTeX built with the New Font Selection Scheme (NFSS), SLiTeX, AmSLaTeX, and so on. Thus, to process documents from various places, a site maintainer was forced to keep multiple versions of the LaTeX program. In addition, when looking at a source file it was not always clear for which format the document was written.
To put an end to this unsatisfactory situation, LaTeX2e has been produced; it brings all such extensions back under a single format and thus prevents the proliferation of mutually incompatible dialects of LaTeX 2.09. With LaTeX2e the `new font selection scheme' is standard and, for example, amsmath (formerly the AmSLaTeX format) or slides (formerly the SLiTeX format) are simply extensions, which may be loaded by documents using the same base format.
The introduction of a new release also made it possible to add a small number of often-requested features and to make the task of writing packages and classes simpler.