pyUmbral is a Python implementation of the Umbral threshold proxy re-encryption scheme. It enables delegating decryption rights for encrypted data through a process where a data owner (Alice) generates re-encryption key fragments that semi-trusted proxies (Ursulas) use to transform ciphertexts, allowing a delegatee (Bob) to decrypt using his private key when a threshold of proxies participate. The library provides core cryptographic primitives including key generation, encryption, decryption, key fragment generation, re-encryption, and verification mechanisms built on elliptic curve cryptography.