RESTful web services have become a fundamental building block of modern enterprise, cloud-native, and mobile applications due to their simplicity, scalability, and interoperability. Their stateless, resource-oriented architecture and reliance on standard HTTP methods enable seamless integration across heterogeneous systems, including microservices, IoT platforms, and serverless environments. However, the widespread adoption of RESTful APIs has significantly expanded the attack surface of enterprise systems, making API security a critical concern. Vulnerabilities such as broken authentication and authorization, insecure token management, injection attacks, excessive data exposure, denial-of-service attacks, and misconfigured transport security frequently lead to data breaches, service disruptions, and regulatory non-compliance. This paper presents a comprehensive review of the security challenges affecting RESTful web services and systematically examines the mechanisms and strategies used to mitigate these threats. Key security solutions, including OAuth 2.0, OpenID Connect, JSON Web Tokens, HTTPS/TLS, mutual TLS, role-based and attribute-based access control, input validation, rate limiting, API gateways, and Web Application Firewalls, are analyzed with respect to their effectiveness, performance impact, and deployment complexity. The study further explores secure implementation strategies within DevSecOps pipelines, emphasizing automated testing, continuous monitoring, and secure API design principles. Performance implications of security enforcement, such as latency overhead, scalability constraints, and resource utilization, are critically evaluated in high-throughput and distributed environments. A comparative analysis of open-source and commercial security solutions highlights trade-offs between flexibility, cost, and operational maturity. Finally, the paper discusses emerging trends and research directions, including AI-driven threat detection, zero-trust architectures, adaptive security policies, decentralized identity, and enhanced observability integration. By consolidating existing knowledge and practical insights, this review provides a holistic framework for designing, implementing, and maintaining secure RESTful web services in complex enterprise and cloud-native systems.