Oregano
Another famed Mediterranean herb, oregano is slightly similar in taste to basil. Oregano will give food a slightly more peppery, floral undertone, but its overall uses are similar.
Thyme
Thyme has a warmer, earthier taste than basil or oregano, but it can still be a viable substitute for basil in most recipes. Select fresh thyme leaves whenever possible.
Celery Leaf
Most people throw away celery leaves instead of using them in recipes, but these delicious leaves are perfect for use as substitutes for basil. Consider mixing them with a small amount of fresh parsley to make the flavor more closely resemble Mediterranean herbs.
Cilantro
Perfect as a substitute for basil, cilantro can give pesto sauce an impressive kick and can help to balance Asian dishes such as Thai curries. Cilantro is the leaf of the plant that yields coriander seeds, and it possesses an exotic flavor.
Mint
In Thai cuisine and some Mediterranean dishes, mild mint leaves can act as viable substitutes for basil in recipes. Choose milder mint varieties and cook them longer than you would cook basil. If you'd like, you can even combine mint with another substitute for basil, such as thyme or celery leaf.