If you ever need to crochet two items together or, more likely, attach a strand of new yarn to an already-finished part of any crochet project, you need the slip stitch. This simplest of stitches is also the glue that holds crochet rounds together. You use a slip stitch to join the last stitch of the round to the first stitch of the round, creating an unbroken ring; you then use one or more chain stitches to start the next ring in the round.
Things You'll Need
Poke your crochet hook through the stitch you want to slip stitch into. If you're using the slip stitch to join two pieces of crochet together, poke your hook through both pieces where you want the join to start.
Yarn over. In other words, wrap the yarn around your crochet hook once from back to front, creating a loop of yarn on the hook.
Draw the hook back through the stitch you're working into, pulling that yarned-over loop with it. If you already had a loop of yarn on your hook, pull the yarned-over loop through that existing loop, too; this completes the slip stitch. If you didn't have a loop of yarn on your hook already, you're only halfway done -- keep reading.
Yarn over again, creating another loop of yarn on your crochet hook. Use the hook to draw this loop back through the loop you just made in the previous step; this completes the slip stitch, securely joining the yarn to your project. You can carry the tail end of the yarn along in your next few stitches, weaving it seamlessly into the project so there's zero risk of the join coming unraveled.
Because a slip stitch is practically invisible, some patterns use a series of slip stitches to move the yarn from one part of a crochet row to the other.
If you’re joining yarn to an already-existing project, you can tie a slipknot and place the loop of the slipknot over your hook instead of doing the first yarn over. You should, however, do any other yarn overs as directed.
If you like working with very old British crochet patterns, you might occasionally encounter a pattern using the term "single crochet," "single stitch" or "close joining stitch" to mean a slip stitch. This is because the same stitches have different names on different sides of the Atlantic, although modern British patterns are more likely to refer to slip stitches as exactly that.