Software-as-a-service (SaaS)

Software-as-a-service (SaaS) is a cloud computing delivery model in which applications are hosted and maintained by a provider and accessed by customers over the internet, typically through a web browser. The provider manages the underlying infrastructure, application runtime, data storage, security, and updates. Customers consume the software on a subscription or pay-as-you-go basis rather than purchasing and installing it on their own hardware.

SaaS is one of the three principal cloud service models, alongside Platform-as-a-service (PaaS) and Function-as-a-service (FaaS). Where PaaS provides a platform for developers to deploy their own applications, and FaaS abstracts even the runtime away into event-triggered functions, SaaS delivers a complete, ready-to-use application directly to end users. Common examples include email services, customer relationship management (CRM) systems, collaboration tools, and feature flag management platforms.

The SaaS model traces its origins to the application service provider (ASP) era of the late 1990s. Salesforce, founded in 1999, is widely credited with establishing the modern SaaS paradigm, launching its CRM product as a web API-accessible service in 2000. The model proliferated as broadband internet access became ubiquitous and virtualization and containerization technologies made multi-tenant hosting economically efficient.

From an architecture perspective, SaaS applications are usually multi-tenant: a single deployment serves many customers, with data isolation maintained at the application or database level rather than through separate infrastructure per customer. This multi-tenancy is what makes SaaS economically viable at scale, since the provider can share infrastructure costs across many subscribers. SaaS products are therefore commonly built as distributed software, often using microservices or other service-oriented architecture styles to support independent scaling of different parts of the system.