Microsoft and Salesforce have been frenemies for 15 years. Here’s a timeline of the rocky history between the tech heavyweights. (MSFT, CRM)

Salesforce’s decision to buy workplace messaging app Slack for $27.7 billion puts the company in head-on competition with long-time frenemy Microsoft.

It’s the latest twist in a long history of partnerships and disputes.

The two tech giants have had a complicated relationship over the years, perhaps starting in the mid-2000s, when former Microsoft CEO Steve Ballmer and Salesforce CEO Marc Benioff traded public jabs. The animosity continued for nearly a decade, until Microsoft named a new CEO, Satya Nadella, who introduced a friendlier Microsoft.

Nadella “opened a door that was closed. And locked. And barricaded,” Benioff said at the time. The companies partnered for the first time, and Nadella even appeared at Salesforce’s big Dreamforce conference. But tensions started to rise once again as Microsoft tried to buy Salesforce in 2015, according to CNBC, and later beat Salesforce in a contentious bid to acquire LinkedIn. 

Buying Slack was a clear move for Salesforce to expand beyond its core customer relationship management products and bring collaboration into the platform, while positioning itself to compete with Microsoft. 

“If Salesforce wants to expand beyond its core gold mine of sales and marketing departments and further into the enterprise, this was the moment and thus represents a major shot across the bow against Microsoft,” Wedbush analyst Dan Ives wrote in a note to clients.

Here’s a look back at the complicated history between Salesforce and Microsoft: