The Book of Ruth in the Bible Encyclopedia - ISBE
1. Order in the Canon:
The place which the Book of Ruth occupies in the order of
the books of the English Bible is not that of the Hebrew
Canon. There it is one of the five meghilloth or Rolls,
which were ordered to be read in the synagogue on 5 special
occasions or festivals during the year.
In printed editions of the Old Testament the megilloth are
usually arranged in the order: Cant, Ruth, Lamentations,
Ecclesiates, Esther. Ruth occupied the second position
because the book was appointed to be read at the Feast of
Weeks which was the second of the 5 special days. In Hebrew
manuscripts, however, the order varies considerably. In
Spanish manuscripts generally, and in one at least of the
German school cited by Dr. Ginsburg (Introduction to the
Hebrew Bible, London, 1897, 4), Ruth precedes Cant; and in
the former Ecclesiastes is placed before Lamentations. The
meghilloth constitute the second portion of the kethubhim or
Haigographa, the third great division of the books of the
Hebrew Scriptures. The Talmud, however, dissociates Ruth
altogether from the remaining meghilloth, and places it
first among the Hagiographa, before the Book of Psalms. By
the Greek translators the book was removed from the position
which it held in the Hebrew Canon, and because it described
events contemporaneous with the Judges, was attached as a
kind of appendix to the latter work. This sequence was
adopted in the Vulgate, and so has passed into all modern
Bibles...
Link: https://bible-history.com/isbe/R/RUTH,+THE+BOOK+OF/