Oh, the drama! Oh, the debate! My answer on the subject? It depends. The publishing world is trending towards a single space after periods, yet not all of the academic world is following suit. See below for specifics.
For the Publishing World
The large publishing houses in the United States are using the Chicago Manual of Style (CMOS). If you are planning to submit a manuscript (or publish one and look more professional) this is the way to go.
“The view at CMOS is that there is no reason for two spaces after a period in published work…it is inefficient, requiring an extra keystroke for every sentence… So, in our efficient, modern world, I think there is no room for two spaces after a period.” More CMOS FAQs here.
I was trained to use two spaces after periods, but am now retraining myself to use a single space to follow current publishing trends. You can look up other CMOS specifications on the Purdue Owl, as well as, on the CMOS site.
For the Academic World
MLA Style (more…)