Evidence-based practice has become the benchmark for quality in healthcare and builds on rules of evidence that have been developed in psychology and other health-care disciplines over many decades. This volume aims to provide clinical neuropsychologists with a practical and approachable reference for skills in evidence-based practice to improve the scientific status of patient care. The core skills involve techniques in critical appraisal of published diagnostic-validity or treatment studies. Critical appraisal skills assist any clinician to evaluate the scientific status of any published study, to identify the patient-relevance of studies with good scientific status, and to calculate individual patient-probability estimates of diagnosis or treatment outcome to guide practice. Initial chapters in this volume review fundamental concepts of construct validity relevant to the assessment of psychopathology and cognitive abilities in neuropsychological populations. These chapters also summarize exciting contemporary development in the theories of personality and psychopathology, and cognitive ability, showing a convergence of theoretical and clinical research to guide clinical practice. Conceptual skills in interpreting construct validity of neuropsychological tests are described in detail in this volume. In addition, a non-mathematical description of the concepts of test score reliability and the neglected topic of interval estimation for individual assessment is provided. As an extension of the concepts of reliability, reliable change indexes are reviewed and the implication of impact on evidence-based practice of test scores reliability and reliable change are described to guide clinicians in their interpretation of test results on single or repeated assessments. Written by some of the foremost experts in the field of clinical neuropsychology and with practical and concrete examples throughout, this volume shows how evidence-based practice is enhanced by reference to good theory, strong construct validity, and better test score reliability.