Flow Studies for Horn by Nancy Sullivan is appropriate for high school through professional horn players.
This old discontinued edition contains 42 etudes. Available while supplies last.
"Nancy Sullivan has compiled and created a wonderful set of exercises which emphasize the one thing horn players are expected to be able to do better than all the other brasses, and that’s legato playing. With these varied and effective exercises, along with the many suggested and recommended variants, any intermediate through professional player will be able to greatly improve their legato prowess." - Douglas Hill, Emeritus Professor of Horn, University of Wisconsin - Madison
56 pages, spiral bound to lay flat on the music stand