Kitchener Stitch

From BluWiki

The kitchener stitch, also known as grafting, is used to make an invisible join between two groups of live stitches.

First, pull a length of yarn at least three times longer than your intended finished edge, cut it, and thread it on a yarn needle. Now go into the first stitch on the front needle as if to purl.

Pull the yarn all the way through. Now go through the first stitch on the back needle as if to knit.

Pull the yarn all the way through. This is the set up.

You will repeat these next four steps across the row.

Go into the first stitch on the front needle as if to knit.

Pull the yarn through and pull the stitch off.

Go into the next stitch on the front needle as if to purl. Pull the yarn through, but leave the stitch on the needle.

Go into the first stitch on the back needle as if it purl.

Pull through and pop the stitch off.

Go into the next stitch on the back needle as if to knit.

Pull the yarn through and leave the stitch on the needle.

The video showing how to do this is here.