What is Multi-tenant SaaS?

Multi-tenancy is an architecture pattern where a single instance of an application serves multiple customers (tenants). Each tenant's data is logically isolated — they can't see or access other tenants' data — but they share the same underlying infrastructure.

This is the standard model for SaaS products. The alternative is single-tenancy, where each customer gets their own dedicated infrastructure. Single-tenancy is more expensive to operate but may be required for regulated industries or enterprise customers with strict data isolation requirements.

There are three main approaches to implementing multi-tenancy: database-per-tenant (highest isolation, highest cost), schema-per-tenant (good balance of isolation and efficiency for moderate scale), and row-level isolation (all tenants in shared tables, distinguished by a tenant_id column — most cost-efficient, requires rigorous query-level filtering to prevent data leaks).