The chapter discusses the importance of validity and reliability in quantitative research studies, particularly for nurses. Validity refers to the accuracy of measuring a concept, while reliability concerns the consistency of measurements. Three types of validity are content validity, which ensures the instrument covers all relevant aspects of the variable; construct validity, which assesses the ability to draw inferences from test scores; and criterion validity, which compares the instrument with other instruments measuring the same variable. Reliability is assessed through homogeneity (internal consistency), stability (test-retest and parallel-form reliability), and equivalence (inter-rater reliability). The chapter emphasizes the importance of these measures in evaluating the quality and applicability of research findings in nursing practice.The chapter discusses the importance of validity and reliability in quantitative research studies, particularly for nurses. Validity refers to the accuracy of measuring a concept, while reliability concerns the consistency of measurements. Three types of validity are content validity, which ensures the instrument covers all relevant aspects of the variable; construct validity, which assesses the ability to draw inferences from test scores; and criterion validity, which compares the instrument with other instruments measuring the same variable. Reliability is assessed through homogeneity (internal consistency), stability (test-retest and parallel-form reliability), and equivalence (inter-rater reliability). The chapter emphasizes the importance of these measures in evaluating the quality and applicability of research findings in nursing practice.