Quick answer
Multi-tenant means one codebase and one database serve many customers, with each customer's data isolated. It is the standard SaaS architecture.
What it is
In a multi-tenant architecture, one deployment of the software serves many customers. Each customer is a tenant; their data is isolated either by row-level security in a shared database or by a separate database per tenant. Multi-tenant scales efficiently and lets the vendor ship features for everyone at once.
Why it matters
Multi-tenant is what makes SaaS economical. Without it, you would deploy a separate instance for every customer, which kills margins and slows shipping.
How to use it
- Design the data model with a tenant_id on every row from day one.
- Use row-level security or middleware to enforce isolation.
- Add observability to detect cross-tenant data leaks.
- Plan for noisy neighbours with rate limits and quotas.
Examples
- Salesforce, Slack and Notion are multi-tenant SaaS.