Slack
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Investors
Founders
About
Slack is an enterprise collaboration and messaging platform that transformed workplace communication. The company originated as Tiny Speck, founded in 2009 by Stewart Butterfield, Cal Henderson, Eric Costello, and Serguei Mourachov — all former colleagues from Flickr 1. Tiny Speck initially built a massively multiplayer online game called Glitch, but the internal communication tool the team built during game development proved more compelling than the game itself 2. Stewart Butterfield had previously co-founded Flickr, which was sold to Yahoo in 2005 1.
Slack launched publicly in February 2014 and grew rapidly, reaching 60,000 daily active users within months 3. By October 2014, the company had over 73,000 paying users and more than $1 million in monthly recurring revenue 4. Slack went public via a direct listing on the New York Stock Exchange on June 20, 2019 5. On July 21, 2021, Salesforce completed its acquisition of Slack for $27.7 billion, one of the largest software deals in history 6.
Funding History
| Round | Date | Amount | Lead Investor(s) | Key Co-Investors | Valuation |
|---|---|---|---|---|---|
| Seed | 2009 | $1.5M | Angel round | Accel, SV Angel, various angels 7 | — |
| Series A | 2010 | $5M | Accel Partners | Andreessen Horowitz 7 | — |
| Series B | Apr 2011 | $10.7M | Accel, Andreessen Horowitz | — 3 | — |
| Series C | Apr 2014 | $42.75M | Social Capital | — 3 | — |
| Series D | Oct 2014 | $120M | Google Ventures, Kleiner Perkins | — 4 | $1.2B |
| Series E | Apr 2015 | $160M | Social Capital | — 8 | $2.76B |
| Series F | Apr 2016 | $200M | Thrive Capital | GGV, Comcast Ventures, Accel, Index Ventures, Social Capital 5 | $2.8B |
| Series G | Sep 2017 | $250M | SoftBank Vision Fund | — 2 | — |
| Series H | Aug 2018 | $427M | Dragoneer, General Atlantic | T. Rowe Price, Wellington Management, Baillie Gifford, Sands Capital 9 | $7.1B |
What Investors Say
Ron Conway, founder of SV Angel, described his investment philosophy that guided his early bet on Slack: “We invest in people first, idea second, market size third. It’s our belief that the idea that we’re seeing is going to morph so much that we should not get wedded to the idea, we should get wed to the individuals” 10.
What Founders Say
Stewart Butterfield shared his philosophy on building Slack: “It’s not enough just to build a great product. You have to put effort into communicating what this does for them, the problem this is solving for them, the outcome this is going to achieve for them” 11.
Butterfield also emphasized sustainable culture, designing Slack’s offices to be empty by 6:30 PM each night with people working approximately 45 hours per week, creating a work environment where employees could “continue building things while still seeing their families grow up” 11.
Sources
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TechCrunch, “The Slack Origin Story,” May 30, 2019. https://techcrunch.com/2019/05/30/the-slack-origin-story/↩↩
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Nira, “How Slack Became a $16 Billion Business by Making Work Less Boring,” accessed March 2026. https://nira.com/slack-history/↩↩
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Clay, “How Much Did Slack Raise? Funding & Key Investors,” accessed March 2026. https://www.clay.com/dossier/slack-funding↩↩↩
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Tracxn, “Slack — 2026 Funding Rounds & List of Investors,” accessed March 2026. https://tracxn.com/d/companies/slack/__1smzz0sCOc6tXojwiPrIG-8Pwh9_z7QN7cXxNCyA5VE/funding-and-investors↩↩
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Slack Technologies, Wikipedia, accessed March 2026. https://en.wikipedia.org/wiki/Slack_Technologies↩↩
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Salesforce, “Salesforce Completes Acquisition of Slack,” July 21, 2021. https://www.salesforce.com/news/press-releases/2021/07/21/salesforce-slack-deal-close/↩
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Crunchbase, “Slack — Seed Round,” accessed March 2026. https://www.crunchbase.com/funding_round/slack-seed–8dbd0e78↩↩
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TechCrunch, “Slack’s In Talks With Coatue, Others For Another Round At A $2.5B Valuation,” March 23, 2015. https://techcrunch.com/2015/03/23/slacks-in-talks-with-coatu-others-for-another-round-at-a-2-5b-valuation/↩
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Enterprise CIO News, “Slack secures $427 million in Series H round,” August 21, 2018. https://www.enterprise-cio.com/news/2018/aug/21/slack-secures-427-million-series-h-round-taking-company-valuation-71-billion/↩
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Medium, “The Ron Conway’s Way,” accessed March 2026. https://medium.com/lombardstreet-io/the-ron-conways-way-8a9224fd63b↩
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Lenny’s Podcast, “Slack founder: Mental models for building products people love ft. Stewart Butterfield,” accessed March 2026. https://www.lennysnewsletter.com/p/slack-founder-stewart-butterfield↩↩