The objective of this article was to (1) review the engineering and medical literature to structure the available information concerning the assessment of spasticity in the neurological population; (2) to discuss the strengths and weaknesses of the different methods currently in use in spasticity assessment; and (3) make recommendations for future efforts in spasticity outcome assessment. Spasticity textbooks, Web sites, and OVID, IEEE, and Medline searches from 1966 through 2003 of spasticity, quantitative measure, or outcome assessment in the rehabilitation population were used as data sources. Over 500 articles were reviewed. Articles that discussed outcome measures used to assess interventions and evaluation of spasticity were included. Authors reviewed the articles looking at inclusion criteria, data collection, methodology, assessment methods, and conclusions for validity and relevance to this article. Issues such as clinical relevance, real-world function and lack of objectivity, and time consumed during performance are important issues for spasticity assessment. Some measures such as the Ashworth Scale remain in common use secondary to ease of use despite their obvious functional limitations. More functional outcome goals are plagued by being more time consuming and a general inability to demonstrate changes after an intervention. This may be secondary to the other factors that combine with spasticity to cause dysfunction at that level. Quantitative metrics can provide more objective measurements but their clinical relevance is sometimes problematic. The assessment of spasticity outcome is still somewhat problematic. Further work is necessary to develop measures that have real-world functional significance to both the individuals being treated and the clinicians. A lack of objectivity is still a problem. In the future it is important for clinicians and the engineers to work together in the development of better outcome measures.