Flavonoids, abundant in plant-based foods such as vegetables and fruits, are widely recognized for their potential to reduce the risk of various chronic diseases, including cardiovascular disorders. Ingested flavonoids are partially absorbed in the intestinal tract, metabolized in the small intestine and liver, and subsequently circulate in the bloodstream. Recent studies have revealed that flavonoids can also be transferred into breast milk during lactation. However, the specific metabolites and concentrations of flavonoids present in breast milk, the mechanisms underlying their transfer from maternal circulation, the potential transfer to infants, and the physiological effects in infants remain poorly understood. This chapter summarizes recent findings and explores the physiological relevance of flavonoids in breast milk.