Abstract
The chapter first briefly recalls the birth and development of matrix theory from the beginning of our era to the end of the 19th century. Then, the attention is paid to the birth of matrix language and the successful establishment of matrix theory in the first three decades of the 20th century, especially in the period between the world wars.
The whole chapter contains brief information about contemporary textbooks and monographs, which were partly or fully devoted to matrices. A very interesting topic is the penetration of matrices into quantum mechanics in the 1920s (so-called matrix quantum mechanics).