Author and Date of Writing
The author is unknown. Jewish tradition points to Samuel, but it is unlikely that he is the author because the mention of David (4:17,22) implies a later date. Further, the literary style of Hebrew used in Ruth suggests that it was written during the period of the monarchy.
Ruth lived during the time of the judges; the book was written sometime after David became king in about 1010 BC.
[Source:NIV Study Bible, Copyright © 1985, 1995, 2002, 2008, 2011 by Zondervan.]