Concerns about the quality of health and mental health services have led to the development and prioritization of implementation science within the portfolio of health services research (Institute of Medicine, 2009a; National Institutes of Health, 2013). The science of implementation has advanced rapidly over the past decade (Chambers, 2012). However, much of the empirical literature has focused on clinician and organizational-level factors and strategies that influence the adoption, implementation, and sustainment of evidence-based practices (EBPs; Aarons, Ehrhart, & Farahnak, 2014; Aarons, Horowitz, Dlugosz, & Ehrhart, 2012; Glisson & Williams, 2015). Despite conceptual literature that points to the importance of system-level influences on adoption, implementation, and sustainment (e.g., Aarons, Hurlburt, & Horwitz, 2011; Damschroder et al., 2009; Flottorp et al., 2013), there is a void in empirical work that attends to this matter. This may be due to the inherent difficulty of studying contexts and strategies within large systems. However, as service systems face increasing pressure to promote the adoption, implementation and sustainment of EBPs, particularly through the passing of the Patient Protection and Affordable Care Act, there is a critical need for empirical research that can inform system-level implementation efforts. The purpose of this special issue is to present a set of articles that can inform system-level implementation research and practice by suggesting how contexts and strategies can be leveraged to promote implementation and quality improvement in behavioral health, and to encourage dialogue and further empirical research in this area.