Multi-tenancy is a widely accepted approach to building SaaS applications. Sharing the database, application and other resources among multiple customers is cost-efficient and makes the system easier to deploy, update and manage. However, developing such a system can be challenging. Determining tenants, isolating a customer’s data from others, and determining and applying an efficient database structure and codebase requires significant experience. As the lead developer of a multi-tenant application framework (https://abp.io), I will talk about how to design a good multi-tenant system, explain the concepts and show concrete examples of implementation details.