Thomas L. Leming joined MCI on April 21, 1971 where, as Vice President of Transmission Systems, he became responsible for the design, planning, and construction of MCI's nationwide microwave network. When MCI began telecommunication operations in 1973, Leming was promoted to Senior Vice President of Transmission Systems. In this capacity he oversaw the construction and operation of MCI's transmission network which came to include not only microwave, but also multiplex and fiber optic systems. Leming was instrumental in realizing the plan to expand MCI's network from a single Chicago-St. Louis route to a system serving telecommunication customers worldwide. He retired from MCI in May 1986.

The records of Thomas Leming consist of correspondence and subject files during Leming's tenure with MCI and earlier years, from 1971 to 1986. Document types include agreements, presentations, transmission maps, and technical reports and memoranda addressing such topics as network expansion, right-of-way, fiber optics, and radio equipment.

The records of the subseries have been arranged in four groups: 1. Correspondence; 2. Subject files; 3. Presentations, reports, and publications; and 4. Channel Usage Graphs.