Study designs form the backbone of scientific research, determining how data are collected, analyzed, and interpreted. They fall into three main categories: experimental, observational, and descriptive. Experimental designs—especially randomized controlled trials—test cause-and-effect relationships through randomization, controls, and blinding. Observational designs such as cohort, case-control, and cross-sectional studies observe exposures and outcomes without intervention, each offering unique strengths and limitations. Descriptive designs, including case reports and case series, document clinical observations and often generate hypotheses. A structured decision-making framework helps researchers match their design to the research question, ethical constraints, available resources, and the level of evidence required.