Microsoft is the parent of LinkedIn, which it acquired in 2016 for about $26.2 billion.
Microsoft announced the LinkedIn acquisition in June 2016 and completed it in December of that year. LinkedIn continued to operate as a distinct service, while Microsoft gained a major professional network containing profiles, recruiting tools, job listings, learning products, and business subscriptions.
LinkedIn was founded in 2003 and launched publicly in 2003. Its network is built around professional identity and employment rather than primarily personal social interaction. That focus made it complementary to Microsoft's enterprise software and cloud businesses.
The acquisition price was an announced transaction value, not Microsoft's market capitalization. Microsoft is a diversified public company whose major businesses include Windows, Office, Azure, gaming, and professional services. LinkedIn is one of its subsidiaries, not a separate parent company controlling Microsoft.