Byzantine agreement, a fundamental problem in distributed computing, enables $N$ processes to reach consensus on a common value despite up to $T < N$ arbitrary failures. It serves as the backbone of critical distributed services such as distributed key generation (DKG), secure multi-party computation (MPC), blockchain technologies, and state machine replication (SMR), highlighting its crucial role in modern computing. Despite their importance, existing agreement protocols face significant limitations. Many struggle to scale efficiently due to poor performance or heavy reliance on cryptographic tools such as threshold signatures, which require expensive setup and computationally intensive algebraic operations. Furthermore, dependence on these “heavyweight” cryptographic primitives weakens their security in a post-quantum world. As agreement protocols continue to grow in scale and importance, there is an urgent need for solutions that are both efficient and resilient to emerging security threats and future technological advancements. In this talk, I will present the first complexity-optimal agreement protocols that either rely only on “lightweight” cryptographic primitives, such as hash functions, or eliminate the need for cryptography entirely. These solutions cover all major network models— asynchrony, partial synchrony, and synchrony—matching or exceeding the best-known results while relying on minimal cryptographic assumptions.