Microsoft is buying the professional networking website LinkedIn for just over $26bn (£18bn) in cash.
The deal will help Microsoft boost sales of its business and email software.
Microsoft said that LinkedIn would retain its "distinct brand, culture and independence".
Ben Wood, head of research at CCS Insight, said the deal would give Microsoft access to the world's biggest professional social network with more than 430 million members worldwide.
Read more: Microsoft to buy LinkedIn for $26bn - BBC News