Slack vs Microsoft Teams: Which Should Your Team Actually Use?

If your organisation already pays for Microsoft 365, Microsoft Teams is almost certainly the right answer, and the burden of proof sits with anyone arguing otherwise. If your work depends on a wide set of third-party tools talking to each other in a channel, or you collaborate constantly with people outside your company, Slack earns its separate line item. This is rarely a contest about which app is nicer to use. It is a contest between an included component of a suite you already own and a specialised tool you would be adding.

The short answer

• Pick Teams if you run Microsoft 365, meetings and calling matter as much as chat, and IT wants one identity, one compliance boundary and one bill.
• Pick Slack if your day runs on integrations — deploys, alerts, tickets, CRM notifications landing in channels — and you want the messaging layer to be the system of record.
• Pick Slack if you work shoulder-to-shoulder with clients, agencies or partners; shared channels with external organisations are its strongest single feature.
• Pick Teams if your headcount includes frontline or deskless staff, or you need webinars and town halls without buying a separate events product.

Where they differ that actually matters

What you are actually buying

Teams is licensed as part of Microsoft 365 for most organisations, alongside a standalone Essentials plan and a free tier with meeting length limits. If your company already has Business Standard or an enterprise plan, Teams is already paid for. Slack is a per-seat subscription in its own right, with a free tier that caps message history at ninety days and integrations at ten. That cap is the real constraint on the free plan: a team that has been running for a year cannot search its own first six months.

This changes the conversation. Slack does not have to be better than Teams. It has to be better than Teams by enough to justify a line of spend you could avoid.

Integrations and the channel as a workspace

Slack’s app directory is enormous and, more importantly, the culture around it is mature: alerting, incident response, code review and support workflows have been built Slack-first for a decade. Workflow Builder handles no-code automation, with conditional branching on higher tiers, and Canvas and Lists let a channel hold documents and tracked items rather than just messages.

Teams integrates well too, but its gravity pulls toward Microsoft. Files live in SharePoint and OneDrive, notes in Loop and OneNote, automation in Power Automate. If your stack is Microsoft, this is a genuine advantage — permissions and retention follow the file rather than being reinvented in the chat tool. If your stack is not Microsoft, you will feel the friction.

External collaboration

Slack Connect is the feature people switch for. Shared channels with another company behave like internal channels: persistent, searchable, no guest accounts to manage. Agencies and companies with tight vendor relationships get real value here. Teams supports external access and guest accounts, and it works, but it is administered as guest identity in your tenant rather than as a lightweight shared space — more governance, and more friction for the outside party.

Meetings, calling and events

This is Teams’ strongest ground. Meetings, webinars and town halls are first-class, with AI-generated notes, live translation and a Teams Phone add-on for telephony. Slack’s Huddles are excellent for what they are — quick, low-ceremony audio and video starting in the channel you are already in — but Slack is not trying to be your conferencing platform or your phone system. Most Slack organisations pair it with Zoom or Google Meet, which is another cost to weigh.

Admin, compliance and the ceiling

Teams inherits the Microsoft 365 admin and compliance stack: retention policies, eDiscovery, information barriers, conditional access, all managed where your IT team already works. Slack has the equivalents — audit logs, legal holds, data residency, HIPAA support — but they sit on its top tier, so a compliance requirement can move you up a plan. Either way, expect this to be an IT decision as much as a team preference.

Side by side

Who each one is really for

Slack is for companies whose work happens in and around software. Product and engineering organisations, agencies with client channels, startups whose tooling changes twice a year. It rewards teams willing to treat channels as infrastructure — naming conventions, alert routing, workflows — and it is noticeably better than Teams at being the place where automated things happen and people respond.

Teams is for organisations already standardised on Microsoft, especially those with a mix of desk and non-desk workers, meeting-heavy cultures, or compliance teams who want one place to set retention. It is not the more elegant chat product, but it is the one that removes a purchase decision, a second identity provider and a separate audit surface.

When neither is the right answer

If your actual problem is that work is invisible — nobody knows what is in progress or who owns it — adding a chat tool makes it worse rather than better, because chat converts decisions into scrollback. The fix is a task or project system where work has an owner and a state, with chat sitting alongside it; our roundup of the best project management software for businesses is the better starting point. Similarly, a small distributed team that mostly needs shared documents and an occasional call may be well served by lighter tools, covered in our guide to team collaboration tools for remote work.

FAQs

Can we run both?

Many organisations do, usually Teams for meetings and company-wide communication with Slack for a specific department. It works, but it splits the searchable record in two and doubles the notification load. If you do it, be explicit about which conversations belong where.

Is Slack’s free plan viable long term?

Only for small groups that do not need history. The ninety-day message limit means your searchable knowledge quietly expires, and the ten-app cap rules out the integration-heavy setups that make Slack worth choosing in the first place. Treat the free plan as an evaluation.

How do the AI features compare?

Both now ship substantial AI: Slack with channel and thread summaries, recaps and enterprise search; Microsoft with Copilot across Teams and the rest of 365. Copilot is generally a paid add-on, and Slack’s more advanced AI sits on higher tiers. Neither is a good reason to switch on its own — check what your existing licence already includes before paying twice.

How hard is migrating from Slack to Teams, or back?

Harder than vendors suggest. Messages, channel structure and files can be moved with tooling, but integrations, workflows and app configurations have to be rebuilt, and years of threaded context rarely survives in a usable form. Plan for the rebuild, and for a period where people look in the wrong place. For a narrower view of what changes on the reporting side, see our comparison of Slack and Teams analytics features.

Licensing bundles and AI capabilities in this category are changing quickly, and what is included versus an add-on shifts more often than either vendor advertises. Check Slack’s and Microsoft’s current plan pages before you decide.