ZDNet reported that the companies were not competing for the same audience, as Teams, at the time, did not let members outside the subscription join the platform, and small businesses and freelancers would have been unlikely to switch. Though Slack is used by 28 companies in the Fortune 100, The Verge wrote executives will question paying for the service if Teams provides a similar function in their company's existing Office 365 subscription at no added cost. Slack ran a full-page advertisement in the New York Times acknowledging the competing service. It was created during an internal hackathon at the company headquarters, and is currently led by Microsoft corporate vice president Brian MacDonald. After the departure of Lu later that year, Microsoft announced Teams to the public as a direct competitor to Slack at an event in New York on November 2, 2016, and was launched worldwide on March 14, 2017. Qi Lu, EVP of Applications and Services, was leading the push to purchase Slack.

On March 4, 2016, Microsoft had considered bidding $8 billion for Slack, but Bill Gates was against the purchase, stating that the firm should instead focus on improving Skype for Business. On August 29, 2007, Microsoft purchased Parlano and its persistent group chat product, MindAlign. As of 2022, it has about 270 million monthly users. Throughout the COVID-19 pandemic, Teams, and other software such as Zoom and Google Meet, gained much interest as many meetings moved to a virtual environment. Teams replaced other Microsoft-operated business messaging and collaboration platforms, including Skype for Business and Microsoft Classroom. Teams primarily competes with the similar service Slack, offering workspace chat and videoconferencing, file storage, and application integration. Microsoft Teams is a proprietary business communication platform developed by Microsoft, as part of the Microsoft 365 family of products. English, Arabic, Bengali, Bulgarian, Catalan, Croatian, Czech, Danish, Dutch, Estonian, Filipino, Finnish, French, German, Greek, Gujarati, Hebrew, Hindi, Hungarian, Icelandic, Indonesian, Italian, Japanese, Kannada, Korean, Latvian, Lithuanian, Malayalam, Marathi, Norwegian Bokmål, Norwegian Nynorsk, Polish, Portuguese, Romanian, Russian, Serbian, Simplified Chinese, Slovak, Slovenian, Spanish, Swedish, Tamil, Telugu, Thai, Traditional Chinese, Turkish, Ukrainian and Vietnamese.

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