This paper presents a conceptual framework and basic principles to develop a classification system for the most common research designs in psychology, based on three strategies: manipulative, associative, and descriptive. The manipulative strategy includes experimental, quasi-experimental, and single-case designs, each with specific requirements for causal analysis. The associative strategy encompasses comparative, predictive, and explanatory studies, which explore functional relationships between variables. The descriptive strategy involves observational and selective studies, focusing on describing phenomena without manipulation or prediction. The paper emphasizes the importance of understanding the design, measurement, and analysis pillars of research, and provides guidelines for selecting appropriate designs, ensuring replicability, and addressing common methodological issues. It also discusses the need for a balanced approach between internal and external validity, and highlights the importance of controlling confounding variables. The classification system is designed to help researchers choose the most suitable design for their research questions, ensuring rigorous and reliable findings.This paper presents a conceptual framework and basic principles to develop a classification system for the most common research designs in psychology, based on three strategies: manipulative, associative, and descriptive. The manipulative strategy includes experimental, quasi-experimental, and single-case designs, each with specific requirements for causal analysis. The associative strategy encompasses comparative, predictive, and explanatory studies, which explore functional relationships between variables. The descriptive strategy involves observational and selective studies, focusing on describing phenomena without manipulation or prediction. The paper emphasizes the importance of understanding the design, measurement, and analysis pillars of research, and provides guidelines for selecting appropriate designs, ensuring replicability, and addressing common methodological issues. It also discusses the need for a balanced approach between internal and external validity, and highlights the importance of controlling confounding variables. The classification system is designed to help researchers choose the most suitable design for their research questions, ensuring rigorous and reliable findings.