One space. The double space is the hallmark of an amateur...or of a pro being ironic.

I was taught in high school to put two spaces after a period.

I usually do when writing to friends, forums, etc.

But I think that in copy one space looks better. Depending on the letter that begins the next sentence, it can look funny. Not always, sometimes it just catches your eye for whatever reason.

Dont know if it really matters though. I dont think there is any "rule" regarding it.

The old double space convention is left over from the typewriter era when all fonts where monospaced (meaning each letter space was the same size, no matter the size of the actual letter).

Since narrow letters could have wide gaps between them, the double space was needed to visually denote a full stop. That's not the case with the fonts we commonly use today.

If you have ever thought a self published book looked amateurish, but couldn't lay your finger on why, the culprit was likely the double space.

Pusateri nailed it. Modern typography with proportional fonts does not require the extra space. The only time you'd use 2 spaces, that I can think of, is if you're using a fixed font and trying to simulate a typewritten letter.

[DELETED]

On the web it's irrelevant... as HTML ignores multiple spaces (regardless of whether you know better).

Pusateri, you've cleared the air. But I think most of us who went to the old school system have been used to the two spaces so much and still find ourselves inserting them. But I'm changing, check this thread. Most automated software programs don't accept two spaces, it is usually a spelling mistake. We just have to change to the IM way of doing things, just like SEO method of writing an article.

I was talking with a Client who works for one of the big newsletter mailers today about this issue. He fires copywriters who insert two spaces between sentences. He said it's a sign of an amateur.

- Rick Duris

Single spacing for sure unless it's done for a specific spacing reason.