The EU eIDAS regulation defines three levels of electronic signature. Each level builds on the previous level.
Electronic Signature (SES): Sometimes referred to as “simple” or “basic” e-signature. Weak link to signer's identity (email or phone number). Document integrity (alternations) not validated.
Advanced Electronic Signature (AES): Uniquely linked to signatory. Can identify the signatory, Document integrity validated.
Qualified Electronic Signature (QES): Highest security and legal validity. Requires an EU-certified and audited Qualified Trust Service Trust Provider (QTSP). The same legal validity of a handwritten (“wet”) signature.