Oracle nodes enable smart contracts to access off-chain and cross-chain data, thus bridging information among digital networks and with the real economy. However, reliance on external input creates security and reliability risks in information aggregation and transfer. We describe the general oracle problem, introduce the Oracle Trilemma – highlighting the trade-offs between scalability, decentralization, and truthfulness – and discuss relevant economic issues concerning the role of oracles in applications such as DeFi, supply chain management, gaming, and prediction markets. In particular, we survey off-chain reporting, off-equilibrium alerting, and dynamic incentive design as promising approaches to resolving the trilemma. We further list oracle vulnerabilities and evaluate oracle sustainability through staking and tokenomics programs. Finally, we highlight empirical studies on how oracle integration affects DeFi adoption, token valuation, liquidity, and system risks. We conclude by presenting emerging trends and suggesting open research questions.