Birefringent crystals can efficiently modulate polarized light and thus play an important role in a series of opticaldevices such as polarized microscopes, optical isolators and polarizers. To obtain birefringent crystals of large birefringence,the key is to search for functional groups with large microscopic polarizability anisotropy based on structure-property relationships. At present, researchers have discovered a variety of functional groups, such as (BO 3 ) 3- , (CO 3 ) 2- , (B 3 O 6 ) 3- , and (C 3 N 3 O 3 ) 3- and further synthesized some excellent birefringent crystals. In this review, we will introduce recent research advances of our team on novel functional groups and birefringent crystals. These birefringent crystals are classified into two categories,namely, inorganic birefringent crystals and organic-inorganic hybrid birefringent crystals. In addition, their crystal structures, optical properties, and structure-property relationships are thoroughly discussed.