LaTeX and multi-column output 

http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/columns.html

Two column output 

Most classes take a [twocolumn] option command switches to single column output and the \twcolumn command switches back, but both commands start a new page.

Putting page-wide items into a two column document can pose problems

  • Figures and tables - See the FAQ entry. http://www.tex.ac.uk/cgi-bin/texfaq2html?label=widefigs

    There are alternative versions of the float environments - in
    two-column documents, figure* provides a floating page-wide figure
    (and table* a page-wide table). The "*"ed float environments can only
    appear at the top of a page, or on a whole page - h or b float
    placement directives are simply ignored.
    Unfortunately, page-wide equations can only be accommodated inside
    float environments. You could include them in figure environments, or
    use the float or ccaption package to define a new float type.
  • Titles and Abstracts - See the FAQ. http://www.tex.ac.uk/cgi-bin/texfaq2html?label=onecolabs

In twocolumn mode, \newpage and \pagebreak start a new column whereas \clearpage and \cleardoublepage always start new pages.

In a twocolumn document, the ftnright package puts footnotes only under the right columns.

Switching between different formats - multicol 

The multicol package lets you change the number of columns in mid-page and its effect can extend over several pages. The columns on the final page are balanced (equal height) by default.

Here's an example of getting 3-column output.

\begin{multicols}{3}{
Put the text here. Maths, tabulars, pictures etc are all ok (but not
figures and tables). Remember to load in the \texttt{multicol}
package at the top of your document.
}
\end{multicols}

Figures present a problem in a multicol environment. See the multicol hints page for details. http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/multicol_hint.html

Balancing columns at the end of a document 

See the LaTeX FAQ. http://www.tex.ac.uk/cgi-bin/texfaq2html?label=balance

Details 

The gap between columns is controlled by \columnsep. The width of the column rule is controlled by \columnseprule.