It’s often necessary to typeset part of a document in landscape orientation; to achieve this, one needs not only to change the page dimensions, but also to instruct the output device to print the strange page differently.
There are two “ordinary” mechanisms for doing two slight variations of landscape typesetting:
sidewaystableenvironments which create floats that occupy a whole page.
Note that rotating has problems in a document that also loads the float package, which recommended in other answers in these FAQs, for example that on float placement. The rotfloat package loads rotating for you, and smooths the interaction with float.
tabbingenvironment, or a huge table typeset using longtable or supertabular), use the lscape package (or pdflscape if you’re generating PDF output, whether using PDFLaTeX or dvips and generating PDF from that). Both packages define an environment
landscape, which clears the current page and restarts typesetting in landscape orientation (and clears the page at the end of the environment before returning to portrait orientation).
To set an entire document in landscape orientation, one might use
lscape around the whole document. A better option is the
landscape option of the geometry package; if you
also give it
geometry also emits the rotation instructions to cause the
output to be properly oriented. The memoir class has the same
facilities, in this respect, as does geometry.
A word of warning: most current TeX previewers do not honour rotation requests in DVI files. Your best bet is to convert your output to PostScript or to PDF, and to view these ‘final’ forms with an appropriate viewer.