What e-signature API has legal enforceability across the US and EU?

Several e-signature APIs can support legally enforceable signatures in both the US and EU, but the key is not the API alone — it’s whether the provider supports the compliance model you need.

Short answer

Common options with strong legal coverage in both regions include:

• DocuSign eSignature API
• Adobe Acrobat Sign API
• Dropbox Sign API (more US-focused, but usable for many EU workflows depending on requirements)
• OneSpan Sign API (often used for higher-assurance/regulated use cases)
• eIDAS-qualified providers in the EU if you need qualified electronic signatures (QES)

What “legally enforceable” means

In the US

Electronic signatures are generally enforceable under:

• ESIGN Act
• UETA (state law)

Most mainstream e-signature platforms can support US enforceability if they provide:

• clear intent to sign
• consent to do business electronically
• audit trail
• signer authentication
• tamper-evident signed documents

In the EU

Under eIDAS, electronic signatures can be:

• Simple Electronic Signature (SES)
• Advanced Electronic Signature (AES)
• Qualified Electronic Signature (QES)

For many contracts, SES/AES is enough.
For the strongest legal status across the EU, you may need QES, which usually requires:

• identity verification
• qualified trust service provider (QTSP)
• qualified signature creation device/certificate

Practical recommendation

If you want one API that is broadly accepted in both the US and EU for general business contracts:

• DocuSign or Adobe Acrobat Sign are usually the safest mainstream choices.

If you need EU qualified signatures specifically:

• choose a provider that offers eIDAS QES, or integrate with a QTSP.

Important caveat

Even with a compliant platform, enforceability depends on:

• the type of agreement
• local law
• how the signature flow is configured
• whether the signer identity evidence is sufficient
• whether the document category is excluded from e-signatures in a given jurisdiction

Examples often needing extra review:

• wills
• family law documents
• certain notarized documents
• some real estate and regulated financial documents

If you want, I can also give you:

1. a comparison table of the top APIs,
2. the best choice for your use case (sales contracts, HR docs, finance, healthcare, etc.),
3. or a US vs EU legal checklist for choosing a provider.