The discipline of applied behavior analysis (ABA) has been instrumental in improving the lives of people who have intellectual and developmental disabilities (ID/DD). Many effective strategies have been validated for teaching adaptive skills, reducing challenging behaviors, and promoting a meaningful quality of life. Concerning assessment and evaluation methods, ABA contributions include functional behavioral assessment (FBA), functional analysis (FA), and single-case research designs. More recently, greater attention has been paid to “systems” level intervention focusing on large scale behavior-change within schools, habilitation settings, and human services organizations. This special issue of the Journal of Physical and Developmental Disabilities concerns contemporary ABA research applications with people who have ID/DD, highlighting the breadth of topics, procedures, and outcomes that characterize current-day practices. The individuals participating in this research were children and adults with autism, mental retardation, traumatic brain injury, physical disabilities, and co-morbid mental illness. The research emphasizes implementation within diverse settings such as school, home, clinic, and extended-care facilities. Four of the 9 articles describe assessment procedures. The study by Richman, Belmont, Kim, Slavin, and Hayner assessed self-reported stress, challenging behavior, and characteristics of autism among children and adults with Cornelia de Lange and Down syndrome. Kleinmann, Luiselli, DiGennaro, Pace, Langone, and Cochran describe a systems approach for assessing interobserver agreement among staff implementing protective holding (therapeutic restraint) within a behavioral J Dev Phys Disabil (2009) 21:441–442 DOI 10.1007/s10882-009-9162-8