What makes an electronic signature legally binding?

"Is this legally binding?" is the first question anyone asks about an electronic signature. The answer in the UK, the United States, the EU, Canada and Australia is that an electronic signature can bind you just as a pen can, and for the same reasons. This guide explains the four things that make any signature work, how an e-signature tool evidences each of them, and where the exceptions are. The legal-validity page has the country-by-country statutes; this guide is about the ideas behind them.

The principle every law shares

Modern e-signature laws descend from the UNCITRAL Model Law on Electronic Commerce (1996) and the Model Law on Electronic Signatures (2001). Their core rule is one of non-discrimination: a signature, record or contract shall not be denied legal effect, validity or enforceability solely because it is in electronic form. You will find that sentence, almost word for word, in the US ESIGN Act (15 U.S.C. §7001(a)), in the Uniform Electronic Transactions Act adopted by 49 states, in Article 25 of the EU's eIDAS Regulation (which the UK retained after Brexit), in Canada's provincial electronic commerce statutes, and in Australia's Electronic Transactions Acts.

The rule is deliberately modest. It does not say electronic signatures are always valid; it says being electronic is not, by itself, a reason to reject one. Whether a particular signature binds a particular person on a particular document still comes down to four questions that would apply to ink as well.

1. Intent to sign

A signature is a mark made with the intention of authenticating a document. The Law Commission of England and Wales put it this way in 2019: an electronic signature is capable in law of executing a document "provided that (i) the person signing intends to authenticate the document and (ii) any formalities relating to execution are satisfied". ESIGN defines an electronic signature as a sound, symbol or process "executed or adopted by a person with the intent to sign the record". Australia's Act requires a method that "indicate[s] the person's intention in respect of the information communicated".

Intent is a question of fact. Evidence that helps: the signer saw the whole document before signing; the fields were clearly labelled as signatures; the signer had to take a deliberate action (draw, type, upload, then press finish) rather than merely open a link; and a way to decline existed and was not used. A signing tool builds all of these into the flow. A name typed into an email can show intent too, but with less to point to later.

2. Agreement to do it electronically

Most laws also ask whether the parties agreed to deal electronically. UETA applies only to transactions where the parties have agreed to conduct them by electronic means, which can be inferred from conduct. ESIGN goes further for consumers: where a statute requires information to be provided to a consumer in writing, electronic delivery satisfies it only if the consumer has affirmatively consented after disclosures about hardware and software requirements, paper copies and withdrawal (§7001(c)). Australia's section 10 requires that the person to whom the signature is given consents to the electronic method.

This is why a good signing page shows an explicit consent checkbox before the first signature and records when it was ticked. It also protects the sender: the signer cannot later say they thought they were just previewing a draft.

3. Attribution: who signed

A signature only binds the person it belongs to, so the question "was it really them?" is central. UETA states the test plainly: an electronic signature is attributable to a person if it was the act of that person, which "may be shown in any manner, including a showing of the efficacy of any security procedure applied". eIDAS's definition of an advanced electronic signature (Article 26) lists the properties that make attribution strong: uniquely linked to the signatory, capable of identifying them, created using data under their sole control, and linked to the data so that later changes are detectable.

Signing tools attribute a signature through a chain of evidence rather than a single proof:

• The invitation went to a named email address that the sender had for this person, and the signing link was unique and unguessable (in AiresDocs, 256 bits of randomness, stored only as a hash).
• An access code, where used, adds a second factor delivered by another channel.
• Each event records the IP address and browser, which can be matched to the person's usual devices and location.
• The signature itself, drawn or typed, is an image the person adopted.
• Surrounding conduct: the person replied from the same address, performed the contract, paid the invoice.

Courts weigh this evidence; they do not require a cryptographic certificate for an ordinary contract. Where a law does require stronger identity assurance (a qualified signature in the EU, for instance), a tool like AiresDocs is not the right instrument.

4. Integrity: what was signed

The final question is whether the document in your hands is the one that was signed. On paper, alterations leave physical traces. Electronically, integrity is shown with a cryptographic hash: a fixed-length fingerprint (SHA-256) of the file, computed when the document is sealed and recorded on the certificate. Change a comma and the hash changes. If the hash of your copy matches the recorded one, the file is byte-for-byte what was produced at completion. AiresDocs records the hash of the original upload as well, so you can also show what the signers were presented with before any fields were filled.

Flattening matters here too: a signing tool should bake the signatures and field values into the page content, not leave them as removable annotations on top of the PDF. Our guide on verifying a signed contract covers the mechanics.

A valid signature is not the same as a binding contract

People sometimes read "legally binding e-signature" as if the signature made the deal. It does not. A signature satisfies the requirement, where one exists, that a document be signed. Whether the agreement binds depends on the rest of contract law: offer and acceptance, consideration (in common-law systems), capacity, lawful purpose, and no vitiating factors such as misrepresentation or duress. Most of the time this is unremarkable: a signed services agreement with a fee is a contract. But an e-signature on a document that is not a contract in the first place (a memo, a draft, a "subject to contract" proposal) does not make it one.

When extra formalities apply

Some documents need more than a signature: a witness, two witnesses, a seal, delivery, notarisation, registration, or a specific level of electronic signature. These are the "formalities relating to execution" in the Law Commission's formula, and they are where electronic signing most often goes wrong. The common ones:

Country by country, briefly

• United Kingdom: Electronic Communications Act 2000 s 7 (admissibility), retained eIDAS Article 25 (non-discrimination), Law Commission 2019 (confirmation for deeds with physical witnessing). Scotland's Requirements of Writing (Scotland) Act 1995 has its own electronic-document rules.
• United States: ESIGN (federal) and UETA (49 states, DC, USVI); New York's ESRA. Consumer-consent rules in §7001(c); exceptions in §7003.
• European Union: eIDAS, directly applicable, with SES, AES and QES levels; national law sets which documents need QES or handwritten form.
• Canada: PIPEDA Part 2 federally; provincial electronic commerce Acts for private contracts, each with an exclusion list (wills, powers of attorney, some land documents).
• Australia: Electronic Transactions Act 1999 (Cth) s 10 and state equivalents: identification, intention, reliability, consent; exemptions by regulation and state law for wills, some deeds and statutory declarations.

Full statutory detail and links are on the legal-validity page.

A practical checklist

1. Is this document type allowed to be signed electronically where it will be enforced? Check the exclusions above. If it is a deed, a will, a land document or a QES document, stop and take advice.
2. Send to the right address, with the right name. Attribution starts with the invitation. Where the stakes justify it, add an access code and tell the signer by phone.
3. Make sure the signer sees everything and consents. Use a tool with an explicit consent step and a decline option.
4. Keep the sealed file and the certificate, plus the emails around it. Do not edit the PDF afterwards; store a copy and work from copies.
5. Record the document ID so the file can be verified later without relying on anyone's memory.

Every AiresDocs document, on the free plan included, is built around these steps: named invitations, optional access codes, consent, an append-only event log, SHA-256 hashes and public verification.

This guide explains how electronic signature law works in general terms and links to the primary sources. It is not legal advice: rules differ by country and document type and they change. For a specific transaction, ask a qualified lawyer in the relevant jurisdiction. Spotted something out of date? Email support@airesdocs.com and we will check it against the source.