In-service training is envisaged as an essential to the librarian's post-professional education. The effectiveness of this particular type of training is shown to be complementary to academic library education, which deals with principles and general practice. Specialized practices and the experience in-service training gives, assume a significance which mere theorizing and background knowledge often fail to bring out. In-service training may serve the further and more important purpose of integrating librarians in their profession; of giving them such a wide scope of experience as to awaken in them various otherwise dormant interests, making them efficient relations officers with a well balanced attitude toward theory and practice. Details such as the working out of in-service training in relation to organization, specialization, the question of salary and leave, the choice of libraries and criteria for their suitability, length of time and techniques of training, are discussed and the need for the establishment of a center for the organization, direction and promotion of all aspects of librarians' post-professional education, is dealt with. The functions of such a Post-professional Study Center would include the proper conduct and supervision of in-service training, planning of courses and encouragement of higher standards of achievement. (Author/NH)