Your Third Party Assessment Organization, or 3PAO, is the independent auditor who performs the assessment that underpins your FedRAMP authorization. You cannot grant your own ATO and you cannot self-assess your way to FedRAMP — an accredited 3PAO has to test your controls, document the findings, and produce the Security Assessment Report (SAR) that the authorizing official reviews.
Choosing the right 3PAO and preparing for the assessment the right way determines whether you hit your ATO target date or slip it by a quarter. This guide explains what 3PAOs do, what the assessment actually looks like week by week, and how to prepare so your first assessment is your last.
What a 3PAO is (and what it is not)
A 3PAO is an independent assessment organization accredited by the American Association for Laboratory Accreditation (A2LA) against FedRAMP’s requirements. A current list is maintained at the FedRAMP Marketplace. Only A2LA-accredited 3PAOs may perform FedRAMP assessments — a general audit firm or consulting partner cannot sign the SAR unless it holds the accreditation.
A 3PAO is not a consultant, a remediation partner, or an advocate. The 3PAO is required to be independent. The firm that writes your System Security Plan (SSP), implements your controls, or advises on your architecture should not also be the firm that assesses you. That means most FedRAMP programs involve at least two partners — a consulting firm that gets you ready, and a 3PAO that assesses you. Some consulting firms (Atlantic Computer Systems included) explicitly do not perform 3PAO work, which makes us unconflicted as your readiness and remediation partner.
What a 3PAO actually does during an assessment
The 3PAO’s deliverables are four documents, each built from testing against the baseline you have targeted (Low, Moderate, or High).
Security Assessment Plan (SAP). Before testing begins, the 3PAO produces a SAP that describes the scope, methodology, testing window, and rules of engagement. The SAP is coordinated with you and, for agency ATOs, with the sponsoring agency.
Security Assessment Report (SAR). The SAR is the final output. It documents every control tested, whether it was implemented as described, any findings of weakness, and the risk level of each finding. The SAR drives your Plan of Action and Milestones (POA&M).
Penetration test report. FedRAMP Moderate and High require an annual independent penetration test. The 3PAO executes the test against a scope that includes external web application, internal network, mobile (if applicable), cloud configuration, and social engineering. The pen test is a separate workstream with its own rules of engagement and report.
Evidence package. Screenshots, configuration exports, interview notes, and any other artifacts collected during testing. The 3PAO retains this for audit; FedRAMP PMO may request samples.
The 3PAO testing methodology
The 3PAO tests against the NIST SP 800-53A assessment methodology. Each control is assessed through some combination of three techniques:
- Examine — review of documentation, policies, configurations, logs, and other artifacts.
- Interview — structured discussions with control owners, engineers, and administrators.
- Test — direct technical validation, such as logging in with test credentials to verify MFA enforcement, attempting unauthorized access to verify denial, or inspecting a configuration to verify a parameter is set correctly.
A single control may require all three techniques. For example, an audit-logging control (AU-2) might require examination of the audit policy, interviews with the SOC team about how logs are reviewed, and testing by generating events and verifying they are captured and alertable.
The typical assessment timeline
A well-prepared Moderate assessment runs roughly 10–14 weeks from SAP approval to SAR delivery. Here is what those weeks typically contain.
Weeks 1–2: Kickoff and SAP. Formal kickoff, scope walkthrough, refinement of boundary and control inheritance claims, and SAP drafting. The SAP requires sign-off before testing begins.
Weeks 3–8: Field assessment. The 3PAO works through the control catalog, examining artifacts, interviewing personnel, and running technical tests. This is the most evidence-intensive phase. Expect a cadence of daily interviews, evidence requests, and follow-up questions. Responsive evidence production is the single biggest factor in timeline.
Weeks 4–10 (overlapping): Penetration test. The pen test typically runs in parallel with the latter part of the field assessment. External, internal, and application testing are distinct phases with their own scoping and rules.
Weeks 9–11: Draft SAR and management response. The 3PAO produces a draft SAR with all findings and risk ratings. You respond with POA&M entries, accepted risks, or disputes of findings. Dispute resolution is a formal process.
Weeks 12–14: Final SAR and closeout. The SAR is finalized and delivered, along with the final pen test report and evidence package. This package plus your SSP, POA&M, and supporting documents form the FedRAMP authorization package that goes to the sponsoring agency or the FedRAMP Joint Authorization Board (JAB).
High-baseline assessments add 3–6 weeks on top of this because of the larger control count and greater testing depth. Assessments that run longer than planned almost always do so because the CSP was not ready — not because the 3PAO moved slowly.
What you need in place before the 3PAO starts
The point of a readiness engagement (and why most CSPs work with a consultant before engaging a 3PAO) is to arrive at the assessment with all of the following in solid shape.
System Security Plan (SSP). A complete, accurate SSP with all controls addressed, all parameters filled in, and all inheritance claims documented. A vague or outdated SSP is the single biggest source of findings.
Control implementation evidence. Screenshots, configuration exports, policy documents, and runbooks mapped to each control. Many CSPs maintain a “control evidence binder” organized by NIST control family. This is not just helpful — it is essential. The 3PAO is going to ask for all of it.
Policies and procedures. Written, approved, distributed, and dated within the last year. Gaps here are often the fastest way to convert an addressable control to a finding.
Boundary diagram and data flow. Accurate, current, at a level of detail that shows where CUI or federal data enters, moves, and leaves your system. Include inherited services, customer responsibilities, and third-party connections.
Vulnerability scan outputs. Authenticated scans of operating systems, web applications, and databases, with POA&M entries for anything high-severity. Unremediated high-severity findings at assessment time become 3PAO findings.
POA&M. A current POA&M with every known weakness, owner, target date, and risk rating. Hiding weaknesses to avoid filling out a POA&M row is the worst possible strategy — the 3PAO will find them, and they will be findings instead of self-identified items.
Incident response, contingency, and configuration management runbooks. Tested. With evidence of the most recent test.
Personnel screening records. Redacted evidence that workforce with logical or physical access has been screened appropriate to their role and the sponsoring agency’s requirements.
The four most expensive preparation mistakes
1. Waiting to engage a 3PAO until you are “ready.” There is no perfect moment of readiness. Engage the 3PAO early enough to lock in the assessment window; 3PAOs book out months in advance, particularly at quarter-end.
2. Treating the SSP as paperwork. A well-written SSP is what the 3PAO uses to build their test plan. A generic SSP with placeholder language and “n/a” in critical fields generates a cascade of examination findings because the 3PAO cannot confirm what you actually do.
3. Letting vulnerabilities accumulate before the assessment. High-severity vulnerabilities outside your POA&M SLA become findings. Every day you delay remediation is a day closer to testing.
4. Skimping on the tabletop exercises. Incident response and contingency plans without recent testing records are nearly always findings. Two well-documented tabletop exercises per year — one for IR, one for CP — are cheap insurance.
3PAO assessment cost
3PAO assessment pricing varies widely based on scope, baseline, and boundary complexity, but reasonable ranges are:
- Moderate: roughly $150,000–$300,000 for the initial assessment, plus the annual pen test and annual assessment thereafter
- High: roughly $250,000–$500,000+ for the initial assessment, with correspondingly higher annual costs
These numbers are inclusive of the SAR, pen test, and evidence work. They do not include your internal engineering cost, the readiness/consulting cost, or the annual continuous-monitoring overhead that follows authorization.
The most expensive 3PAO engagement is the one that has to be repeated because you were not ready the first time.
How Atlantic Computer Systems supports you through a 3PAO assessment
We are not a 3PAO, and we do not sell 3PAO services. That is deliberate: it makes us unconflicted as your readiness partner. We help CSPs build the SSP, implement and harden the controls, prepare the evidence package, run tabletop exercises, clean up vulnerabilities, and coach your team through the 3PAO’s evidence requests and interviews. When your 3PAO shows up, you will be ready — and when findings come back, we help you work through POA&M remediation to get to ATO.
Request a free FedRAMP readiness assessment →
Related reading:
- FedRAMP Moderate vs High: How to Pick the Right Baseline
- Government IT services
- Cybersecurity services
Last updated: April 2026. This post is educational and does not constitute legal or compliance advice. Baselines, assessment methodologies, pricing ranges, and FedRAMP program details evolve; confirm current requirements at fedramp.gov and with your sponsoring agency.