MongoDB has introduced Client-Side Field Level Encryption (FLE) in version 4.2, allowing selective encryption of individual document fields on the client-side, providing an additional layer of security and compliance with regulations such as GDPR and CCPA. FLE is transparent to the server and handled exclusively within the MongoDB drivers on the client, making it a different approach than column encryption used in relational databases. It is useful for regulatory compliance, managed database services, and protecting sensitive data such as personally identifiable information. The FAQ section addresses common questions about performance impact, relationship with regular at-rest encryption, query support, key rotation, and compatibility with key management solutions. To start using FLE, it's recommended to live migrate existing unencrypted data into a new MongoDB cluster with FLE enabled on relevant fields.