Clinical trials are the foundation of medical research, assessing the efficacy and safety of new therapies before market approval and registration. They follow structured phases (I-IV), from early safety assessments to large-scale efficacy trials and post-market surveillance. Regulatory agencies such as the FDA and EMA enforce strict compliance with Good Clinical Practice (GCP). Recent trends, including decentralized clinical trials (DCTs) and digital health technologies, enhance trial efficiency and patient engagement. Observational studies complement randomized controlled trials (RCTs) by capturing real-world data. The growing focus on patient-centric approaches ensures trials address meaningful clinical outcomes, improving recruitment, retention, and patient experience.