may refer to:
- MCI Inc. , a former American telecommunications company acquired by Verizon Communications
- Microwave Communications Inc., later MCI Communications , the corporation that operated as MCI from 1963–1998
- MCI WorldCom , a previous name for MCI, Inc. , a former US telecom company
- Motor Coach Industries , a coach bus company
- MCI (audio) , a company that manufactured multi-track audiotape recorders and mixing consoles for professional studio recording
- MCI Group Holdings , an event, communication and association management company
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