Robert's Rules of Order
Official editions

Title
Edition
Year
Authors (posthumous authorial credit in italics)
Publisher
Pocket Manual of Rules of Order for Deliberative Assemblies: Robert's Rules of Order
First
1876
Major Henry M. Robert
S. C. Griggs & Company
Pocket Manual of Rules of Order for Deliberative Assemblies: Robert's Rules of Order
Second
1876
Major Henry M. Robert (Lieut. Colonel in later printings)
S. C. Griggs & Company
Pocket Manual of Rules of Order for Deliberative Assemblies: Robert's Rules of Order
Third
1893
Lieut. Colonel Henry M. Robert (Colonel, then General in later printings)
S. C. Griggs & Company (Scott, Foresman and Company in later printings)
Robert's Rules of Order Revised
Fourth
1915
General Henry M. Robert
Scott, Foresman and Company
Robert's Rules of Order Revised
Fifth
1943
General Henry M. Robert (Editors: Isabel H. Robert and Sarah Corbin Robert, Trustee)
Scott, Foresman and Company
Robert's Rules of Order Revised
Sixth
1951
General Henry M. Robert (Editors: Isabel H. Robert and Sarah Corbin Robert, Trustee)
Scott, Foresman and Company
Robert's Rules of Order Newly Revised
Seventh
1970
General Henry M. Robert and Sarah Corbin Robert with the assistance of Henry M.
Scott, Foresman and Company
Robert's Rules of Order Newly Revised
Eighth
1981
General Henry M. Robert and Sarah Corbin Robert with the assistance of Henry M.
Scott, Foresman and Company
Robert's Rules of Order Newly Revised
Ninth
1990
General Henry M. Robert and Sarah Corbin Robert with the assistance of Henry M. Robert III and William J. Evans
Scott, Foresman and Company
Robert's Rules of Order Newly Revised
Tenth
2000
General Henry M. Robert, Sarah Corbin Robert, Henry M.
Perseus Books
Robert's Rules of Order Newly Revised
Eleventh
2011
General Henry M. Robert, Sarah Corbin Robert, Henry M.
Da Capo Press, A Member of the Perseus Books Group

Question: When was the last time that Robert's Rules of Order is revised?
Answer: The Eleventh edition of the series was published in 2011 under the title Robert's Rules of Order Newly Revised.