There are various techniques for joining crochet pieces with an invisible seam, but as I like simplicity I'm going to show you a way that can be done from both the wrong and right sides of the piece. In the example below, the piece is positioned with the wrong side facing up, but it can be done on both sides, it just depends on the result you want. If you do it from the right side of the work, that is, with the right side facing you, the result will be reverse mattress stitch, which also has a very nice effect. See here how to do the reverse mattress stitch. It's very easy to make mattress stitch seam on...