This study examines educators' and providers' perceptions of constraints and critical success factors of the development and implementation of online L2 learning. The focus is on Dutch L2 learning in adult education in Flanders. Semi-structured interviews with seven educators (shaping pedagogies/curricula) and six providers (organizing/offering language programmes) were conducted. Consequently, a focus group consisting of 12 teachers of Dutch (L2) and teacher trainers was run. The findings show that the main perceived constraints of the design and implementation of an online curriculum are negative beliefs about the effectiveness of online language learning, costs, a lack of technical and pedagogical support and insufficient teacher ICT-skills. The perceived major critical success factors are course design, technological facilities, (technical, financial and pedagogical) support, learner skills and attitudes, and competencies of instructional designers. Although many literature references were found concerning the importance of assessment, teacher skills and the role of the faculties, these were hardly mentioned during the interviews. The findings of this study call for a better financial framework, more collaboration among different stakeholders in the field, a focus on online teacher skills, adequate pedagogical and technical support and for a framework for quality assurance in online language learning.