The teacher is the most important factor in the school; the selection of teachers is the most important and difficult duty of school officers. Public funds and children must be guarded against incompetent teachers. To do this, all the States of the Union have by law provided for the examination of applicants and for some form of license or certification for those who pass the examination in such a way as to indicate their fitness to teach and their ability to manage schools. This study was undertaken originally at the request of the first conference of chief State education officers regarding the recognition in each State of teachers' certificate and of diplomas of educational institutions issued in other States. All licenses to teach in the public schools of the United States, except those issued by city boards of education in accordance with conditions prescribed by such boards are embraced in this study. The fundamental purpose of the study is to answer the question, What is the exact status of the legal provisions relating to certification of teachers in the various States at the present time in such a way as to furnish data in the best form for use in the construction of standards of measurement for certificates and in the preparation of standards systems of certification. Acts of Various Legislatures Passed during the Winter of 1911 and not Referred to in Table 1 are appended. Bibliography and index are included. (Contains 10 figures and 34 tables.) [Best copy available has been provided.].