The essay describes the origin and functioning of the largest scientific library in Europe, the National Lending Library for Science and Technology in Britain, (NLL). This Library lends almost entirely by mail, at a rate approaching one million items per year. After outlining the origins of the NLL in government circles shortly after World War II, it attempts to present the picture of its operations today under the following heads: Coverage and Acquisition; Principles of Storage; Records; Techniques of Postal Lending; Personnel Structure; The Reading Room; Russian Translating Program; The Educational Campaign. Some prospects for the future are surveyed in the conclusion. Throughout the essay, emphasis is laid on the innovative approach of the library's first Director, Dr. D. J. Urquhart, and the successes his techniques have had in coping with the national problem of disseminating scientific information in Britain. A bibliography is included. (Author/SJ)