Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, software, telecommunications equipment and other high-technology services and products. Cisco specializes in specific tech markets, such as the Internet of Things (IoT), domain security, videoconferencing, and energy management with leading products including Webex, OpenDNS, Jabber, Duo Security, and Jasper. Cisco is one of the largest technology companies in the world ranking 74 on the Fortune 100 with over $51 billion in revenue and nearly 80,000 employees.

Cisco Systems was founded in December 1984 by Leonard Bosack and Sandy Lerner, two Stanford University computer scientists who had been instrumental in connecting computers at Stanford. They pioneered the concept of a local area network (LAN) being used to connect distant computers over a multiprotocol router system. By the time the company went public in 1990, Cisco had a market capitalization of $224 million; by the end of the dot-com bubble in the year 2000, this had increased to $500 billion, surpassing Microsoft as the world's most valuable company. As of December 2021, Cisco had a market capitalization of around $267 billion.

Cisco stock (CSCO) was added to the Dow Jones Industrial Average on June 8, 2009, and is also included in the S&P 500 Index, the Russell 1000 Index, NASDAQ-100 Index and the Russell 1000 Growth Stock Index.

In 2021, Fortune ranked Cisco number one for the second year on their annual list of the 100 Best Companies to Work For based on employee satisfaction surveying. LinkedIn and Glassdoor also ranked Cisco as a top place to work in 2021 and recent years.