Minuscule 121 (in the Gregory-Aland numbering), ô 258 (Soden), is a Greek minuscule manuscript of the New Testament, on parchment leaves. Palaeographically it has been assigned to the 12th century. It has full marginalia.
The codex contains the text of the New Testament, except Book of Revelation, on 222 parchment leaves (size ) with some lacunae (Acts 1:1-14; 21:15-22:28; 1 John 4:20-Jude End; Romans 1:1-7:13; 1 Cor 2:7-14:23).
The text is written in one column per page, 30-32 lines per page (size of text 12.4 by 9 cm). The initial letters in red.
The text is divided according to the (chapters), whose numbers are given at the margin, and their (titles of chapters) at the top of the pages. There is also a division according to the Ammonian Sections (in Mark 234 - 16:8), with references to the Eusebian Canons (written below Ammonian Section numbers).
It contains the Eusebian Canon tables, the tables of the (tables of contents) before each book, lectionary markings at the margin (for liturgical use), numbers of , Menologion to the Acts, Catholic and Pauline epistles, and the Euthalian Apparatus.
The order of books: Gospels, Acts, Catholic epistles and Pauline epistles.
The Greek text of the codex is a representative of the Byzantine text-type. Hermann von Soden classified it to the textual family K<sup>1</sup>. Aland placed it in Category V.
According to the Claremont Profile Method it represents textual family K<sup>x</sup> in Luke 1, Luke 10, and Luke 20.
Some corrections were made by other hand.
The manuscript was written by Basilius, a monk and diakon. It was examined by Griesbach. C. R. Gregory saw it in 1888.
It is currently housed at the Bibliotheek der Rijksuniversiteit (B. P. Gr. 74<sup>a</sup>), at Leiden.