Research on Access Control Mechanisms in Cloud Computing focuses on managing and regulating user access to cloud resources to ensure confidentiality, integrity, and compliance. Modern approaches integrate role-based, attribute-based, and policy-based access control models, often enhanced with cryptographic techniques and blockchain-enabled frameworks to provide decentralized and tamper-proof authorization. Advanced systems leverage artificial intelligence and dynamic trust evaluation to adapt access policies in real time, accommodating evolving user behavior and threat landscapes. Zero-trust architectures and federated identity management further strengthen security by continuously verifying user credentials and access rights across heterogeneous cloud environments. Overall, effective access control mechanisms in the cloud ensure secure, flexible, and auditable resource access while mitigating insider threats, unauthorized usage, and data breaches.