It depends. If you want extravagant eyebrows, you should absolutely use a primer. As with any eye product, eyebrow products are prone to fading. A primer creates a barrier between the pigment and your skin/hair so the eyebrow product will last longer. But if you want a natural or fluffy look, a primer isn't necessary since you're not working with a pigmented product. Just use your eyebrow pencil or gel of choice. If desired, you can use a topcoat gel to set your brow in place instead of a primer.