A Business Associate Agreement is the contract HIPAA requires between a covered entity (a healthcare provider, health plan, or healthcare clearinghouse) and any vendor that creates, receives, maintains, or transmits protected health information on its behalf. It also applies between a business associate and any subcontractor that touches PHI in the course of the engagement.
The required content is mandated by 45 CFR § 164.504(e). The BAA must permit and limit the business associate's uses and disclosures of PHI, require appropriate safeguards, require breach reporting to the covered entity, require the business associate to ensure that any subcontractors agree to the same terms, allow the covered entity to access and amend PHI on a data-subject's behalf, and require return or destruction of PHI at the end of the engagement.
In SaaS, the BAA usually rides as an exhibit to the MSA, alongside the DPA. For vendors that serve healthcare customers, having a clean, signable BAA on file is table stakes. For vendors that do not yet serve healthcare but might, drafting one in advance is much cheaper than scrambling for one in the middle of an enterprise procurement cycle.
The frequent drafting trap is treating the BAA as a privacy document and stopping there. HIPAA has a security rule with specific technical and administrative safeguards (encryption, access controls, audit logs, incident response) that the BAA presumes are already in place. A BAA without a real underlying security program is a paper compliance exercise that will not survive an OCR investigation.