Choose a healthy basil plant to cut from. You'll want a plant that's mature but not yet flowering.
With a clean, sharp scissors, cut a 4-inch stem from the parent plant right below a leaf node, which is where a leaf joins the stem and where new roots will sprout.
Remove the leaves on the lower part of the stem, leaving just a few sets of leaves at the top.
Put the stem in a glass of clean water, ensuring the leaf nodes are submerged. Place the glass in a location that gets indirect light.
Change the water every other day to keep it clean and free from bacteria.
In a week or two, you should see roots start to grow from the submerged leaf nodes. Once the roots are about 2 inches long, the cutting is ready to be planted.
Plant the rooted cutting in a pot with potting soil. Keep the soil moist but not waterlogged.
Allow the plant to grow and mature before you start harvesting. Always harvest by pinching off a few leaves at a time.