Hyphens, en and em dashes are three visually similar yet significantly different punctuation marks that commonly appear in text. Their definition and purpose are frequently misunderstood by designers and writers alike, often leading to inaccurate and unprofessional typography. While some of this confusion is a result of typewriter conventions still being used in today’s digital world, it is ultimately up to the person doing the typesetting—whether it be a production artist, web programmer, or graphic designer—to get it right.
Ilene Strizver has a great write-up at CreativePro about when to use each, complete with pretty pictures for us designers!