Supervision by circular letters is essential in most counties. The size of the territory to be covered makes frequent visits on the part of the county superintendent an impossibility. Many superintendents have no supervisors or field deputies and have only occasional office help. In such cases circular letters are the most valuable means of supervision. One Iowa county superintendent writes: This county is 48 by 54 miles and has about 150 teachers actually under my supervision. I depend very largely upon circular letters because I can get to a school only once a year unless the teacher is in trouble or I go to make a talk." Many problems individual to teachers or schools can be settled only by conference or correspondence. On the other hand, many difficulties encountered are common to the majority of rural schools and can often be taken care of through circular letters. This bulletin has been prepared to show that there are various types of circular letters which have proved effective in rural-school supervision. It will indicate certain characteristics which tend to increase the value of circular letters. Finally it will demonstrate the use of circular letters as a supervisory agency by including copies of 64 letters written by education officers during the past few years. These letters, collected by Jessie Parker, a member of the Iowa staff, fall into nine categories, as follows: (1) Inspirational letters; (2) Letters to prepare teachers and others to profit by certain supervisory agencies; (3) Follow-up letters; (4) Letters relating to the curriculum; (5) Letters to promote specific educational campaigns and to report progress in connection therewith; (6) Letters to improve the quality of programs of various kinds; (7) Letters including administrative information of special interest to teachers; (8) Letters to pupils designed to further their progress along certain lines; and (9) Routine letters. (Contains 6 tables.) [Best copy available has been provided.]