The paper presents a brief review of the present state of borate crystal chemistry, including ways of describing boron - oxygen rigid groups, the statistics of their occurrence in borates and two current borate classification schemes. One of them by Hawthorne, Burns & Grice is based on the dimensionality of boron - oxygen complexes; the primary division of the other by Strunz is based on the number of boron atoms in the repeat unit of the borate anions (monoborates, diborates, etc.). New original data on the crystal structures, polymorphic transitions and thermal expansion of borates and their relationship to borate glasses are presented.