Double Stitch (German Short Rows)

After turning the work, bring the working yarn to the front and slip the just-worked stitch purlwise to the right needle. Tug on the working yarn, bringing it up and over the needle, around the back, so that the just-worked stitch is pulled up tight, and two strands are sitting on the needle (this is the double stitch).

If the next stitch is a knit stitch, leave the yarn at the back, keeping the tension, and begin to work the instructions following double stitch.
If the next stitch is a purl stitch, bring the yarn around the needle to the front, as if for a yarnover, keeping the tension and work back according to the row’s directions.

When working past a double stitch, knit or purl the double stitch as one stitch through both loops.

You can find a videotutorial here.