Clearly the product description indicates that these socks are recommended for up to Size 9.5.  I wear a Size 10 but still they are comfy enough to wear albeit a bit snug.  These socks are perfect for saving the insoles of my favorite leather shoes.  Today I am wearing them with my Keen sandals and you can't even see them.  They absolutely do not slip down under foot.  The material is bamboo so these socks breathe and wick moisture, a good combination for healthy feet and nails. I found a pin hole in one of the socks just under the elastic. I contacted the seller and she was awesome.  Sent me a replacement pair and then some.  I actually just placed an order for another set of four. I recommend either hand washing or  machine wash at hand-wash or gentle setting.  I also dried mine in the machine at low heat setting.