This chapter introduces lattice-based cryptography for IoT and cloud security. Lattice-based encryption begins with the Shortest Vector Problem (SVP) and Learning With Errors (LWE) difficulties. We then compare lattice-based encryption to RSA and elliptic curve cryptography and discuss its pros and cons. Finally, we introduce "Lattice-based secure data aggregation" for IoT and cloud systems. Lattice-based cryptography ensures data confidentiality and integrity during aggregation. We discuss data encryption, aggregation, and decryption, as well as implementation on resource-constrained devices. Finally, we evaluate the algorithm’s performance and security against other data aggregation algorithms. Our method provides good security against attacks, efficient computations, and low memory requirements. We also discuss the approach’s drawbacks and future research. We introduce lattice-based cryptography, its uses in IoT and cloud security, and a new algorithm for secure data aggregation. In privacy-and security-sensitive IoT and cloud systems, the proposed method could be widely adopted.