What it means
End-to-end encryption (E2EE) means a message is encrypted on the sender's device using a key only the recipient holds, transmitted in encrypted form, and decrypted only on the recipient's device. Crucially, the messaging platform (Meta, in WhatsApp's case) cannot read the message while it is in transit, because they do not have the decryption key.
Consumer WhatsApp uses E2EE by default. The WhatsApp Business app inherits it. The WhatsApp Business API has a more nuanced model: messages are still E2EE between the user and Meta's servers, but business systems (the BSP's inbox, your CRM) need to read messages to function, so they re-encrypt and store messages on the business side.
Why it matters
E2EE is one of WhatsApp's strongest differentiators against SMS, email, and other messaging channels. For sensitive customer communications (medical, financial, personal), it is meaningful protection.
For businesses, the practical implication is that compliance audits should distinguish between transit (E2EE, handled by WhatsApp) and rest (handled by your BSP and CRM, which must encrypt at rest and follow your data-protection rules).
Example
A healthcare clinic asks how patient messages are protected on WhatsApp. The answer: in transit between the patient's phone and Meta's servers, end-to-end encrypted (Meta cannot read them). In the clinic's respond.io inbox, encrypted at rest (respond.io's databases, with AWS infrastructure encryption underneath). Two distinct layers, both required for full protection.