Will I have to get a chain tensioner?

i'm new to singlespeeding and was wondering if it was possible to singlespeed a modern bike without using a chain tensioner,or should i possibly look into getting an old frame with horizontal drop outs and follow that route.

Magic gear, phantom gear, adjustable stays, ebb.. or read the advice offer by Donut! along with Search. mtbr.com used to have a really good SS faq.. try finding that.

Here it is: http://www.mtbr.com/ssfaqcrx.aspx