The purpose of this study was to identify the most important perceived enablers and barriers regarding sustainability of School-wide Positive Behavioral Interventions and Supports (SWPBIS). School personnel representing 860 schools implementing or preparing to implement SWPBIS completed an open-ended survey of factors regarding its sustainability. Qualitative analyses were used to assess perceptions of the most important factors related to sustainability. Thematic analysis produced 13 themes regarding enablers and/or barriers. The most commonly cited enablers were Staff Buy-in, School Administrator Support, and Consistency. The most commonly cited barriers were Staff Buy-in, Resources: Time, and Resources: Money. Results are discussed in terms of enhancing durability of evidence-based practices in schools. [This article was published in "Behavioral Disorders," v40 n3 p171-183 May 2015 (EJ1072245).]