FUNCTION

The question mark is placed at the end of a question.

HISTORY

In Latin texts dating back to the 16th century, questions were marked with a letter Q above an o (as an abbreviation of quaestio, ‘question’ in Latin). It has evolved over the centuries into the simplified form that we know today.

DESIGN

The question mark has to have enough presence in a text to be visible fairly quickly. In the Latin script, it has about the same height and width as a capital letter. Its design has to be related with other glyphs of the typeface, where the top terminal relates to the terminal of other glyphs in the typeface (such as 2, f or C) and the dot below is identical to the period.

TYPOGRAPHIC RULES

In English and all other languages based in the Latin script, there is no space before the question mark, French is the only exception where there is a thin non-breaking space before it.
In Spanish, a reversed question mark is placed at the beginning of the question and the upright one at the end, with no spaces in between the characters and the words.