Multi-tenancy is an architectural design pattern crucial for building scalable and cost-effective B2B SaaS products, allowing a single application instance to serve multiple organizations while keeping their data and workflows isolated. This approach is exemplified by platforms like Slack and Shopify, which offer isolated experiences for each tenant without maintaining separate applications for each customer. Multi-tenancy enables faster feature rollouts, cost efficiency, true scalability, and the ability to accommodate diverse and complex business requirements. Failure to implement multi-tenancy from the outset can lead to significant challenges, including complex database migrations, monitoring difficulties, resource scaling issues, and intricate disaster recovery processes. Examples of multi-tenancy in action include collaborative workspaces, robust organizational dashboards, customizable roles and permissions, and org-specific authentication flows, all of which are essential for serving B2B customers with diverse needs efficiently from a shared infrastructure.