You may see patterns that talk about selvage stitches (sometimes spelled "selvedge") and wonder what they could be referring to. All fabric has selvages; they are simply the left and right edges of the piece, or the first and last stitch of each row.
Some patterns specify to work a selvage stitch; you may notice that directions tell you to always knit the first and last stitch of the row or to slip the last stitch of each row. In these cases, the designer has factored in the selvage as part of the design to make it easier for you. However, if you're creating your own design from a stitch dictionary or just winging it, understanding how to work those selvage stitches (or identify them, if you're modifying a pattern), will be very helpful.
1. Selvages for Seaming
When you have pieces you are going to seam together, such as the front to the back of a sweater, you will use these edge stitches for seaming. They won't be visible after the project is seamed. This is particularly useful when you're creating your own design for a sweater or shrug, which may otherwise end up with yarn-overs and decreases on the edges of the design. Regardless of the pattern stitch used, if you work a stockinette selvage it will make seaming much easier. To do so, simply knit the first and last stitch of every row on the right side and purl them on the wrong side. If a stitch pattern is used, you might check and be sure that the pattern has allowed two extra stitches for seaming so you have a full repeat across after seaming.