Text/Typographical Layout
http://www.webaim.org/techniques/textlayout/

WebAIM
2005

Abstract:

The default setting in browsers is to align text to the left. Text can also be aligned to the right, in the center, or justified (aligned on both the left and the right sides). Although some people like the look of justified text, studies have routinely shown that left-aligned text is the easiest to read. Some Asian and Middle Eastern languages are notable exceptions to this rule, since the normal text direction in these languages may be vertical from top to bottom or horizontal from right to left. For English and other left-top-right languages, the best practice is to align text on the left.