Walnuts are one of the most important tree nuts, belonging to the Juglandaceae family. They are cultivated worldwide, primarily in temperate regions. Throughout history, walnut kernels have been utilized to treat various disorders such as diarrhea, diabetes mellitus, thyroid issues, cancer, anorexia, and infectious diseases, in addition to their dietary benefits. Presently, advanced techniques are employed to identify key compounds in walnuts. The bioactive compounds in walnuts are classified into phenolic acids, tannins and related compounds, flavonoids, phytosterols, fatty acids, tocopherols, vitamins, and carotenoids. The important compounds discussed in this chapter have shown to possess significant medicinal applications. In conclusion, different varieties of walnuts are abundant in significant bioactive compounds that possess important medicinal properties.