Yarn over in crochet is the motion of wrapping working yarn over your hook before pulling it through a loop, repeated constantly across nearly every stitch type. I still remember how mechanical this motion felt at first before it became automatic. This guide covers how it works.

How It Works
Wrap the yarn from back to front over the hook, then pull that wrapped yarn through whatever loop or loops are currently on the hook. Single crochet uses one yarn over per stitch, half double crochet uses two, and double crochet uses two as well but with an extra initial yarn over before inserting the hook.

Frequently asked questions
Why do some stitches need a yarn over before inserting the hook?
Taller stitches like double crochet and half double crochet need an extra initial yarn over before inserting the hook, which is what gives them their added height compared to single crochet.
Ready to learn the hdc stitch?
See how yarn over applies specifically to half double crochet.
Learn to make an hdc stitch