Software as a service (SaaS) is a way of delivering software in which the vendor runs the application on its own servers and customers reach it through a web browser or an application programming interface (API), paying a recurring fee rather than buying a licence and installing a copy. The customer never handles servers, operating systems or upgrades. The model exists because installed enterprise software was expensive to deploy, slow to update and hard to scale, and because a vendor that hosts one copy of its code for thousands of customers can spread those costs across all of them.

Most marketing tools are delivered this way, from customer relationship management (CRM) systems and email platforms to ad servers and programmatic buying platforms.

The formal definition

The reference definition comes from the US National Institute of Standards and Technology (NIST). Special Publication 800-145, written by Peter Mell and Tim Grance and published in September 2011, describes SaaS as "the capability provided to the consumer to use the provider's applications running on a cloud infrastructure". Under that definition the consumer "does not manage or control the underlying cloud infrastructure including network, servers, operating systems, storage, or even individual application capabilities", with the possible exception of limited user-specific settings.

NIST places SaaS on top of two other service models. Infrastructure as a service (IaaS) rents raw compute, storage and networking. Platform as a service (PaaS) adds managed tools on which customers build their own applications. The same document lists five essential characteristics of cloud services: on-demand self-service, broad network access, resource pooling, rapid elasticity and measured service.

How it works

The defining technical feature is multi-tenancy. One running instance of the application, and usually one shared database layer, serves many customers, each logically separated from the others. Salesforce described its Apex programming language, released in 2006, as running on a "multi-tenant, shared architecture". Because there is a single codebase, the vendor ships updates to every customer at once, often several times a year or continuously, rather than waiting for each client to install a new version.

Customers interact through three layers. The user interface is the browser application staff log into. The API lets other systems read and write data programmatically, which is how a CRM passes leads to an ad platform or how a reporting tool pulls campaign data. Integrations, increasingly built on authorisation standards such as OAuth, connect one SaaS product to another without sharing passwords.

Commercially, SaaS runs on contracts rather than purchases. A master subscription agreement sets the terms, and a service level agreement (SLA) commits the vendor to an availability target. The arithmetic matters: an SLA of 99.9% permits roughly 43 minutes of downtime in a 30-day month, while 99.99% permits about four. Pricing generally takes one of three forms. Per-seat pricing charges for each named user. Tiered pricing bundles features and volumes, such as contacts in an email platform. Usage-based pricing charges for consumption, for example API calls, records processed or, in advertising, a percentage of media spend. Revenue is recognised over the life of the contract, which is why SaaS businesses report annual recurring revenue alongside audited figures.

Responsibility is split. The vendor secures the infrastructure and application; the customer controls access, approved integrations and data configuration.

SaaS in advertising technology

Programmatic platforms are largely SaaS products, though they rarely charge like one. Most demand-side platforms (DSPs) take a share of media spend instead of a flat licence fee. A Needham & Co analysis cited by the Wall Street Journal placed The Trade Desk's take rate at 12% to 15%, against about 1% for Amazon DSP. A smaller group sold pure software access. Beeswax, founded in 2014, charged a flat fee based on technology usage for what it called Bidder-as-a-Service; FreeWheel bought it in a deal announced in December 2020.

A percentage fee rises with spend whether or not the software does more work; a seat or usage fee decouples software cost from media cost. The same tension runs through martech, where Scott Brinker's landscape counted 15,505 products in May 2026, almost all sold by subscription.

Origin and evolution

The idea predates the term. Time-sharing bureaus in the 1960s rented central computers to multiple clients, and in the late 1990s application service providers (ASPs) hosted packaged software, often one installation per customer, with limited success. Salesforce, founded in March 1999 in San Francisco, launched its CRM product in 2000 with a "No Software" advertising campaign and went public in June 2004. Its AppExchange marketplace followed in 2005.

By May 2005, eWeek reported that "software as a service" had replaced ASP as the industry's preferred label. IDC estimated SaaS sales would grow from $2.1 billion in 2002 to $8.1 billion in 2008, according to the same report.

The incumbents did move. Amazon Web Services launched its S3 storage service in March 2006, providing infrastructure on which new SaaS vendors could build. Google Apps arrived in August 2006, Microsoft launched Office 365 in June 2011, and Adobe announced on May 6, 2013 that Creative Cloud subscriptions would replace boxed Creative Suite sales.

Scale followed. Gartner forecast on November 19, 2024 that worldwide end-user spending on SaaS would reach $299.1 billion in 2025, up 19.2% from $250.8 billion in 2024. That made SaaS larger than IaaS ($211.9 billion) or PaaS ($208.6 billion) in the same forecast, though growing more slowly than both.

Why it matters for marketers

Every new marketing tool adds a subscription, a login and a copy of customer data, and per-seat economics reward vendors for adding users. Software agents now test that model. When Salesforce unveiled Headless 360 on April 15, 2026, exposing its platform through APIs, Model Context Protocol (MCP) tools and command-line commands, it also said it was moving Agentforce from per-seat licensing to consumption-based pricing. In Gartner's 2026 CMO Spend Survey, 56% of respondents had increased spending on consumption-based martech, while 9% had cut it.

The programmatic market faces the same question. Ari Paparo, founder of Marketecture Media, argued in July 2025 that agentic AI could take over campaign setup and targeting, the work for which DSP users currently pay.

Limitations and disputes

Lock-in is the oldest complaint: data, workflows and integrations accumulate inside one vendor. The EU Data Act, applicable from September 12, 2025, requires data processing providers to support switching, and from January 12, 2027 it bans switching charges, including egress fees. Spain's competition authority found that only 2.3% of sampled business customers switched infrastructure or platform provider between 2022 and 2024, though its study excluded SaaS as a separate, more fragmented market.

Subscription practices draw regulators. The US Department of Justice, acting for the Federal Trade Commission, sued Adobe in June 2024, alleging that customers on its "annual paid monthly" plan faced an early termination fee of up to 50% of remaining payments that was not clearly disclosed. Adobe denied wrongdoing; in March 2026 it agreed to pay $75 million to the government and provide $75 million in free services to some customers, according to Fox Television Stations' report of the settlement.

Security depends on the weakest connected app. Between August 8 and 18, 2025, attackers tracked by Google as UNC6395 used stolen OAuth tokens from the Drift chatbot to query Salesforce data across hundreds of corporate instances, among them Cloudflare, Palo Alto Networks and Zscaler. The weak point was the trust granted to a connected app, not a password.

AI substitution became a market dispute in early 2026. After Anthropic released plugins for its Claude Cowork agent covering legal, finance, marketing and data work, software shares fell sharply. London Stock Exchange Group dropped almost 13% on February 3, 2026, and Publicis and WPP fell almost 5% and 3.3% the next morning, according to Reuters. "The sector isn't just guilty until proven innocent but is now being sentenced before trial," said Toby Ogg, an analyst at JP Morgan. Nvidia chief executive Jensen Huang called the idea that AI would replace software companies "the most illogical thing in the world", according to Forbes. By mid-April the iShares Expanded Tech-Software Sector exchange-traded fund was about 28% below its September 2025 peak.

Not the same as

IaaS and PaaS. These rent infrastructure or development platforms; the customer still builds and runs the application. Hyperscalers such as Amazon, Microsoft and Google sell all three layers, which blurs the line in billing but not in responsibility.

Application service provider. An ASP hosted conventional software, typically one installation per client. SaaS is built for many tenants on a single codebase from the start.

Managed service. A managed service bundles software with people who operate it. Amazon's managed DSP offering, for example, carries a 15% service fee plus a 10% platform fee, while self-serve access leaves the operation to the buyer.

Cloud. Cloud describes the delivery infrastructure; SaaS is one commercial model built on it. Licensed software installed on rented cloud servers is not SaaS.

Recent developments

The pressure on SaaS in 2026 has come from agents rather than rivals. Anthropic launched Cowork on January 12, 2026, bringing file and workflow automation to non-developers. Traffic to automation platforms Zapier, n8n and Make fell by double digits over twelve weeks to August 2026, according to an a16z analysis. Salesforce released seven prebuilt agents and a long-horizon runtime on September 11, 2026, without announcing their pricing.

In advertising, Microsoft discontinued its Microsoft Invest DSP on February 28, 2026, saying the current DSP model could not deliver its agentic plans. The Trade Desk reported second-quarter 2026 revenue of $715 million, up 3%, as rivals offered agent-built deals at fees near 1%.

Timeline

  • 1960s: Time-sharing bureaus rent shared computers to multiple clients
  • Late 1990s: Application service providers host packaged software for businesses
  • March 1999: Salesforce is founded in San Francisco
  • 2000: Salesforce launches its CRM product with the "No Software" campaign
  • June 2004: Salesforce goes public
  • 2005: Salesforce launches AppExchange
  • May 25, 2005: eWeek reports SaaS replacing ASP as the industry label
  • March 2006: Amazon Web Services launches S3
  • August 2006: Google Apps launches
  • June 2011: Microsoft launches Office 365
  • September 2011: NIST publishes SP 800-145 defining SaaS, PaaS and IaaS
  • May 6, 2013: Adobe moves Creative Suite to Creative Cloud subscriptions
  • 2014: Beeswax launches Bidder-as-a-Service
  • June 2024: DOJ sues Adobe on behalf of the FTC over subscription terms
  • November 19, 2024: Gartner forecasts $299.1 billion SaaS spending for 2025
  • August 8-18, 2025: Drift OAuth tokens used to access Salesforce instances
  • September 12, 2025: EU Data Act becomes applicable
  • January 12, 2026: Anthropic launches Cowork
  • February 3-4, 2026: Global software share sell-off after Anthropic's Cowork plugins
  • February 28, 2026: Microsoft Invest DSP discontinued
  • March 2026: Adobe settles the FTC case for $75 million plus $75 million in services
  • April 15, 2026: Salesforce unveils Headless 360 and consumption pricing for Agentforce
  • September 11, 2026: Salesforce releases seven prebuilt agents
  • January 12, 2027: Data Act ban on switching charges takes effect

Summary

Who: Software vendors such as Salesforce, Adobe, Microsoft and Google, ad tech platforms including The Trade Desk, Amazon DSP and Beeswax, and the marketers, agencies and publishers that subscribe to them. NIST defined the model; the FTC and the European Union regulate how it is sold and switched.

What: A delivery model in which the provider hosts, runs and updates an application for many customers on shared infrastructure, accessed through a browser or API and paid for by seat, tier or usage.

When: Rooted in 1960s time-sharing and 1990s ASPs, popularised by Salesforce from 2000, formally defined by NIST in September 2011, and under pressure from AI agents and consumption pricing since early 2026.

Where: Across enterprise software and marketing technology, from CRM and email platforms to DSPs and ad servers, with the EU Data Act setting switching rules in Europe.

Why: Hosting one codebase for many tenants lowers deployment cost and speeds updates for buyers, while giving vendors predictable recurring revenue. The same structure creates lock-in, subscription disputes and exposure if agents can do the work that seats pay for.