eCTD Structure for Clinical Submissions

The electronic Common Technical Document (eCTD) organizes every FDA drug and biologic submission into the same five-module folder hierarchy, whether the filing is an Investigational New Drug (IND) application, a New Drug Application (NDA), an Abbreviated New Drug Application (ANDA), or a Biologics License Application (BLA). Getting that structure right — the module boundaries, the regional content in Module 1, and the XML backbone that ties the folders together — is what determines whether FDA’s Electronic Submissions Gateway (ESG) accepts a sequence or technically rejects it before a reviewer ever opens the file. This guide covers the module-by-module structure, how it differs from the underlying Common Technical Document (CTD) content standard, current FDA specification-version requirements, and the structural checks that cause most first-time rejections.

The eCTD module hierarchy at a glance

Module	Content	Harmonized by ICH?	Typical FDA contents
Module 1	Administrative and regional information	No — region-specific	FDA Form 1571 (IND cover sheet), FDA Form 356h (NDA/ANDA/BLA), labeling, meeting requests, annual reports
Module 2	CTD summaries	Yes	Quality Overall Summary; Nonclinical Overview/Summary; Clinical Overview/Summary
Module 3	Quality (CMC)	Yes — ICH M4Q	Chemistry, manufacturing, and controls data for drug substance and drug product
Module 4	Nonclinical study reports	Yes — ICH M4S	Pharmacology, pharmacokinetics, toxicology study reports
Module 5	Clinical study reports	Yes — ICH M4E	Protocols, Clinical Study Reports (CSRs), other clinical data

Modules 2 through 5 follow the same content organization in every ICH region — the same submission structure applies whether it goes to FDA, EMA, or another ICH regulatory authority. Module 1 is the exception: each regulatory authority defines its own Module 1 requirements, so a sequence built for FDA cannot simply be re-filed with EMA or Japan’s PMDA without rebuilding Module 1 to that authority’s specification.

eCTD vs. CTD: structure vs. format

These two terms get used interchangeably, but they describe different things. The Common Technical Document (CTD) is the ICH-harmonized content and organization standard — what goes in each module and in what order. The eCTD is the electronic implementation of that same structure: a fixed folder tree plus an XML backbone file (index.xml) that gives reviewers a hyperlinked table of contents and assigns a lifecycle operation to every file in the submission. Because essentially all NDA, ANDA, BLA, and IND traffic to FDA today is filed electronically, the CTD as a standalone paper format is rarely seen in practice — but the module numbering and content rules it defines are exactly what the eCTD folder tree implements.

Module 1: what goes in the region-specific module

Module 1 is where sponsors most often build submissions incorrectly, because it is the one module ICH does not standardize. For FDA specifically, Module 1 holds:

• The application’s cover form — FDA Form 1571 for an IND, or FDA Form 356h for an NDA, ANDA, or BLA
• Administrative correspondence: meeting requests, annual reports, amendments
• Labeling
• Investigator-level documentation such as FDA Form 1572 (Statement of Investigator), where applicable to the submission type

Other ICH regulatory authorities define their own Module 1 content and folder conventions independently — the EU submission process (managed through EMA) and Japan’s PMDA process each specify their own regional Module 1 documents and metadata. A sequence built to FDA’s Module 1 specification is not portable to another region’s Module 1 without rework; only Modules 2-5 carry over directly.

The XML backbone and lifecycle operations

What makes a set of folders an eCTD, rather than just an organized electronic submission, is the backbone: an index.xml file and related metadata that sits on top of the Module 1-5 tree. The backbone does two things a plain folder structure cannot do on its own:

• Builds the navigable table of contents reviewers use to move through the submission, hyperlinking every leaf document to its place in the module structure.
• Assigns a lifecycle operation to each file — new, append, replace, or delete — so a sponsor can submit an amendment, a safety update, or a new study report as an incremental addition to the application’s existing submission history rather than resubmitting the entire dossier every time.

Submissions are numbered sequentially (sequence 0000 for the original application, 0001 for the next submission tied to it, and so on), and each new sequence’s backbone references the prior sequence it modifies. Getting the lifecycle operation wrong on a single leaf — marking a corrected document as new instead of replace, for example — is one of the most common structural errors in practice, because it breaks the document’s version history inside the application without necessarily producing an obvious error at submission time.

Which eCTD specification version to use

FDA currently supports two eCTD specification versions in parallel: v3.2.2, the long-standing specification most submissions still use, and v4.0, which FDA’s Center for Drug Evaluation and Research (CDER) and Center for Biologics Evaluation and Research (CBER) began accepting for new NDA, BLA, ANDA, IND, and Master File submissions on September 16, 2024. As of this writing, v4.0 support is limited to new applications only — forward-compatibility functionality that would let an existing v3.2.2 application transition to v4.0 is not yet available, and FDA has not set a date for phasing out v3.2.2. Which version a specific submission must use is set by the FDA Data Standards Catalog, and FDA publishes updates to supported versions through the Federal Register.

Last verified 2026-08-16 against FDA’s Electronic Common Technical Document (eCTD) page (fda.gov), content current as of 10/04/2024 per FDA’s own page footer — reconfirm before treating the v4.0 date as current if this page is read well after that.

Who is required to submit in eCTD format

FDA’s electronic submission requirements phased in by application type. Filing in eCTD format is mandatory for:

• NDAs, ANDAs, and BLAs (mandatory since May 5, 2017)
• Commercial INDs — those intended to eventually support marketing (mandatory since May 5, 2018)
• All subsequent submissions to any of the above application types — amendments, supplements, annual reports — even if the original application predates the mandate
• Master files, including Drug Master Files (DMFs), which are treated as submissions to the IND, NDA, ANDA, or BLA they support

Electronic submission in eCTD format is optional but encouraged for noncommercial INDs (investigator-sponsored and expanded-access INDs), submissions involving blood and blood components (including source plasma), and Type III Master Files.

Why submissions get technically rejected

FDA’s ESG validates the structure of an eCTD sequence on receipt, and a sequence that fails that validation is rejected rather than routed to a reviewer — which means a structural error costs a full resubmission cycle, not just a correction note. The categories of error that most often cause a technical rejection, based on FDA’s published eCTD guidance and conformance documentation, include:

• Invalid or missing backbone. The index.xml file must validate against the DTD for the specification version (v3.2.2 or v4.0) the sequence is built to.
• Incorrect lifecycle operations. A leaf marked new when it should replace an existing file (or vice versa) breaks the document’s version history within the application.
• Missing or incomplete Module 1 regional content — an application-type cover form that isn’t included, or required administrative metadata left blank.
• Non-conformant PDFs — documents missing bookmarks/hyperlinks, security-restricted PDFs that block text extraction, or non-searchable scanned pages where searchable text is expected.
• Sequence and folder-naming errors — sequence numbers that don’t follow the required four-digit format, or folder names that don’t match the DTD-defined structure.

FDA publishes the current eCTD Guidance and version-specific Technical Conformance Guides directly on its Electronic Common Technical Document page; because validation rules are tied to the specification version and are updated periodically, treat the categories above as the recurring pattern of failure rather than an exhaustive rule list, and check FDA’s current conformance guide for the specific submission before filing.

A structural checklist before submission

1. Confirm which specification version (v3.2.2 or v4.0) applies to this application per the FDA Data Standards Catalog — don’t assume based on a prior submission to the same application.
2. Validate the sequence locally against the applicable DTD before transmitting it — most eCTD-authoring/publishing tools include this check.
3. Verify every Module 1 regional document required for this submission type is present (cover form, labeling, correspondence) and correctly placed.
4. Check the lifecycle operation assigned to every leaf, especially in amendments — new vs. replace vs. append vs. delete.
5. Confirm the sequence number is the next unused number for this application and correctly references the prior sequence.
6. Confirm all PDFs are bookmarked, hyperlinked where cross-referenced, and free of security restrictions that block extraction.
7. Submit through an active FDA ESG account and confirm receipt via FDA’s acknowledgment messages before treating the submission as complete.

Frequently asked questions

What are the five modules of eCTD?

Module 1 (administrative and regional information), Module 2 (CTD summaries), Module 3 (quality/CMC), Module 4 (nonclinical study reports), and Module 5 (clinical study reports). Modules 2-5 are harmonized across ICH regions; Module 1 is defined separately by each regulatory authority.

What’s the difference between the CTD and the eCTD?

The CTD is the ICH-harmonized content and organization standard. The eCTD is the electronic, XML-backboned implementation of that same structure, used for actual submission and lifecycle management with a regulatory authority such as FDA.

Does FDA require eCTD v3.2.2 or v4.0?

Both are currently supported. FDA began accepting v4.0 for new NDA, BLA, ANDA, IND, and Master File submissions on September 16, 2024, but v4.0 does not yet support transitioning an existing application forward from v3.2.2, and FDA has not announced a date for retiring v3.2.2. Confirm the required version for a specific application against the current FDA Data Standards Catalog.

Is eCTD mandatory for all IND submissions?

No. eCTD format is mandatory for commercial INDs (products intended to eventually support marketing), effective May 5, 2018. Noncommercial INDs — investigator-sponsored and expanded-access INDs — are not required to file electronically, though FDA encourages it.

What happens if an eCTD sequence fails validation?

FDA’s Electronic Submissions Gateway validates the structure on receipt. A sequence with an invalid or missing backbone, incorrect lifecycle operations, or missing required Module 1 content is technically rejected rather than passed to a reviewer, which typically means correcting the structural error and resubmitting the sequence.

Related CASRAI resources

See CASRAI’s dictionary entries on eCTD and the ICH M4 (CTD) guideline family for the underlying content standard, the Investigational New Drug (IND) application and FDA Form 1571 guide for what Module 1 accompanies on an IND, and the FDA Pre-IND Meeting and ICH M11 Clinical Trial Protocol Template guides for adjacent steps in building a regulatory submission. For the broader regulatory-submission landscape, see the Clinical Research Administration pillar.