Flavonoids are polyphenolic phytocompounds with pronounced medicinal properties. Flavonoids are known to have potent anticancer potential. Flavonoids work by acting on various signaling pathways that regulate cancer pathophysiology. Flavonoids, because of their antioxidant, proapoptotic, antiproliferative, and anti-inflammatory properties, combat the various complications of cancer. Flavonoids mitigate the growth and aggravation of neoplastic cells. By their antiproliferative effect, flavonoids restrict the division and expansion of cancer cells. And by proapoptotic effect, flavonoids stimulate the signaling pathways associated with programmed cell death and induce cellular apoptosis. This chapter focuses on the antiproliferative and also the proapoptotic effects of flavonoids as anticancer agents and the underlying molecular mechanism. This chapter also includes challenges and opportunities of using flavonoids in oncotherapy and the future scope of using flavonoids in cancer therapy.