The short answer:
But there are hundreds of different fonts, and what you use is up to you. Factors to consider in choosing fonts are:
Some fonts are naturally more comfortable for people to read. Excessively narrow or wide text, for example, may require the reader to slow down and reread, or may be overlooked altogether. Serifs help our eyes identify letters quickly, but heavy or ornate serifs have the opposite effect. Sans-serif fonts, likewise, vary from the clear and simple to the nearly abstract. Most fonts are more readable at certain sizes than at others. When working with a new font, print out a draft of some of your text, as the appearance of fonts on your screen is only an approximation of how they will look on paper.
You may want to use more than one font within a document, tailoring the appearance to fit the purpose of different blocks of text. Look through the course textbook and notice how different fonts, sizes, and colors have been used to distinguish between titles, narrative, footers, examples, definitions, and so forth.
If your document contains numerals, especially numerals mixed with letters (such as serial numbers or part numbers), you'll want a font in which a capital letter O is distinguishable from the numeral zero (0), and in which small L (l) and one (1) and capital I (I) are all distinguishable. Fonts that are very stylized and simplified can be ambiguous.
Text that is in ALL CAPS (all capital letters), such as a title or poster heading, will be most effective in a simple font without strong serifs or flourishes. Use all-capitals sparingly, as it is much easier for people to read words written in lower-case letters (with or without initial capitals), than many adjacent capital letters. Furthermore, capitals can seem VERY LOUD – EVEN AGGRESSIVE – to the reader.
Use a non-proportional font, such as Courier, for columns of numbers so that they will line up vertically when read. All words or spaces preceding those numbers (after the most recent paragraph or tab character) should be in the same non-proportional font.
A font can make text seem more formal, friendly, elegant, bouncy, trendy, stodgy, calm, threatening, quiet, brash - there is a host of unspoken associations we make with fonts because of the ways they've been used throughout our culture. A traffic summons and an invitation to a fundraising ball could be printed in the same font, but they aren't. Why? Pay attention to how each font will be "felt" by your readers, and choose fonts that help convey your chosen message.
As a general rule, use only one or two different fonts in a small or simple document. And remember that you can always change fonts and font sizes of your text anytime you wish. Since they're so easy to change and experiment with, feel free to explore the different fonts available to you. Soon you'll discover favorites that work well for you in different circumstances.
Copyright 1996 by the Curators of the University of Missouri