A master services agreement sets the general legal terms of a vendor relationship, liability, confidentiality, payment terms in general. A SOW sits underneath it and defines one specific piece of work: what gets delivered, by when, against what milestones, and for how much. A single vendor relationship can have many SOWs over time under one master agreement.

Billing against a SOW is rarely a flat recurring charge. It can be time-and-materials, fixed-price milestones, or volumetric, and each type requires validating the invoice against a different part of the SOW's terms before approving payment.

Frequently Asked Questions

How is a SOW different from a purchase order?

A SOW is a contractual document describing scope and deliverables for services, often spanning months. A purchase order is typically the transactional authorization to pay against it, and one SOW may correspond to multiple POs over its life.

Why is SOW billing harder to automate than product invoicing?

Because the billing basis varies by contract, hours worked, milestones hit, volume delivered, and validating an invoice means checking it against the specific terms of that particular SOW rather than a single universal rule that applies to every vendor the same way.

What data does a SOW-billing AI agent need access to?

The SOW's own rate cards and terms, plus whatever delivery evidence proves the work was actually done, timesheets, milestone sign-offs, delivery confirmations, depending on the specific billing type.

Can multiple SOWs exist under a single vendor contract at once?

Yes, and this is common for large service providers, one master agreement can govern dozens of active SOWs simultaneously, each with its own scope, timeline, and billing terms, which is part of why complex enterprise billing operations are hard to run manually at scale.