An eCTD submission's structure is largely defined by the primary standard created by the International Council for Harmonisation (ICH). However, additional specifications may be applied in national and continental contexts. In the United States, the Food and Drug Administration (FDA) layers additional specifications onto its requirements for eCTD submissions, including PDF, transmission, file format, and supportive file specifications. In the European Union, the European Medicines Agency's EU Module 1 specification, as well as other QA documents, lay out additional requirements for eCTD submissions.

eCTD has five modules:

• Administrative information and prescribing information
• Common technical document summaries
• Quality
• Nonclinical study reports
• Clinical study reports

There are two categories of modules:

• Regional module: 1 (different for each region; i.e., country)
• Common modules: 2–5 (common to all the regions)

The CTD defines the content only of the common modules. The contents of the Regional Module 1 are defined by each of the ICH regions (USA, Europe, and Japan).

The electronic common technical document