There are many ways to work successful buttonholes. For the Wicked Eyelet Rib Vest, Joëlle used a yarn-over to create a buttonhole. The yarn-over buttonhole works especially well with finer yarns; it makes a perfect opening for small to average size buttons and it can be worked while knitting the piece, thus eliminating some of the finishing work. For larger buttonholes, try the Bound-Off Buttonhole.
To make this type of buttonhole, the yarn-over creates extra stitch to create the hole for the button. This means that one stitch must also be eliminated at this point to keep the number of stitches consistent. This is accomplished by either k2tog or p2tog (depending on the stitch pattern you are working in) after the yarn-over. On the next row the yarn-over and the decrease stitches are worked as previously established in the pattern. In the Wicked Eyelet Rib Vest the buttonholes are worked every 12 rows, making it easy to keep track of their placement.