Standardized outcome measures (OMs) are a vital part of evidence-based practice. Despite the recognition of the importance of OMs, recent evidence suggests that the use of OMs in clinical practice is limited. Selecting the most appropriate OM enhances clinical practice by (1) identifying and quantifying body function and structure limitations; (2) formulating the evaluation, diagnosis, and prognosis; (3) informing the plan of care; and (4) helping to evaluate the success of physical therapy interventions. This article (Part I) is the first of a 2-part series on the process of selecting OMs in neurological clinical practice. We introduce a decision-making framework to guide the selection of OMs and discuss 6 main factors-what to measure, the purpose of the measure, the type of measure, patient and clinic factors, psychometric factors, and feasibility-that should be considered when selecting OMs for clinical use. The framework will then be applied to a patient case in Part II of the series (see the article "Outcome Measures in Neurological Physical Therapy Practice: Part II. A Patient-Centered Process" in this issue).