This chapter focuses on outcome measurement in relation to intervention evaluation. Measuring the outcome of health care is 'a central component of determining therapeutic effectiveness and, therefore, the provision of evidence-based healthcare'. Information regarding the outcome of neuropsychological rehabilitation is not only important for researchers, clinicians, managers and policy makers, but especially for the patients and their families. Neuropsychologists often conduct extensive testing during pre-treatment assessment, but in clinical practice it is less common to measure outcome systematically after treatment. The instruments are presented and organised according to the framework of the International Classification of Functioning (ICF), Disability and Health. Special emphasis is placed on level of participation as an important goal of rehabilitation. In addition, criteria for choosing an outcome measure are presented, and finally some recent developments in outcome measurement are discussed. In measuring the outcome of neuropsychological rehabilitation, not all domains of the ICF are relevant to neurological disorders.