Since ancient times, medicinal plants have been employed as reliable and important sources of bioactive compounds and to treat several diseases and ailments. Despite the significant advances in synthetic drugs, side effects remain, which necessitates the search for effective, inexpensive, and more accessible drugs. Medicinal plants may provide such valuable therapeutic alternatives. In this respect, Cinchona officinalis is a medicinal plant, and one of several Cinchona species used for the production of quinine, among other compounds, which is an anti-fever agent and is especially useful in the prevention and treatment of malaria. Similarly, Corylus avellana, the common hazel, is a species of hazel that is native to Europe and western Asia, Greece, Turkey, and Cyprus. Hazel contains significant amounts of thiamine and vitamin B6, as well as smaller amounts of other B vitamins, and is an excellent source of vitamins E and B6. Additionally, hazel contains taxol, a widely used anticancer drug, originally extracted from the bark of taxus. Similarly, Cinchona is a genus of flowering plants belonging to the family Rubiaceae. Plants of this genus have been used in the traditional medicine of several cultures to treat numerous diseases such as fever, cancer, and digestive issues as anti-protozoal and anti-spasmodic, digestive tonic and for the treatment of cardiac diseases. This is due to the presence of phytochemicals including quinine, quinidine, cinchonine, and cinchonidine. Thus, the aim of the present chapter is to provide updated information on the two medicinal plants, Cinchona spp. and C. avellana. In this chapter, the most recent literature pertaining to their use in traditional medicine, chemical derivatives, and potential benefits for humans are summarized.