If your company is growing, acquiring other businesses, or even thinking about selling a division one day, you need to make one Microsoft 365 decision carefully from day one: do you run everything in a single tenant, or do you separate businesses into multiple tenants? In this video I break down what a Microsoft 365 tenant actually is (your organization’s container in the Microsoft cloud) and I clear up the biggest confusion I see all the time: your tenant is not your domain and it’s not your subscription. You can have multiple domains and multiple subscriptions inside one tenant, and adding a domain means verifying it with DNS records. Then I walk you through the real pros and cons of single-tenant vs multi-tenant architecture for 2026 planning. For most small and medium businesses, a single tenant with multiple domains is the simplest and most efficient approach: one admin portal, unified security policies, easier collaboration, and centralized billing. But if you manage separate businesses, plan acquisitions, or may sell/spin off a brand later, a multi-tenant strategy can save you months of migration work. When each business already lives in its own tenant, separating it later can be as simple as transferring administrative control—no mailbox, OneDrive, SharePoint, or Teams migrations, and far less risk of downtime.