BACKGROUND: Factors influencing the implementation of communication partner training (CPT) with familiar partners of people with aphasia (PWA) have previously been documented using disparate approaches. To date there has been no synthesis of these factors using a common theoretical framework. Investigating CPT implementation factors using a common theoretical framework may further our understanding of universal barriers and guide future development of tailored, theoretically informed implementation strategies. AIMS: (1) To determine the perceived and/or observed barriers and facilitators to implementing CPT with familiar partners of adults with aphasia; (2) to map extracted barriers and facilitators to a common theoretical framework; (3) to synthesize extracted barriers and facilitators; and (4) to identify potential implementation strategies to address the most frequently identified barriers and facilitators. METHODS & PROCEDURES: A systematic review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Four electronic databases (MEDLINE, EMBASE, CINAHL, Web of Science) were systematically searched in April 2021. Empirical qualitative and/or quantitative research studies reporting barriers/facilitators to speech-language therapists (SLTs) implementing CPT with familiar partners of adults with aphasia were included. The search was limited to English or French articles with no date limit applied. Methodological quality of included studies was assessed using the Mixed-Methods Appraisal Tool (MMAT). A framework and content analysis was then conducted to extract and synthesize the implementation factors in alignment with the Theoretical Domains Framework (TDF), followed by a theoretically informed mapping exercise to identify potential implementation strategies. RESULTS & MAIN CONTRIBUTION: The database searches yielded 2115 studies. Following screening, 17 studies were included in the review. Overall, the included studies had good methodological quality. Extracted implementation factors were classified as barriers, facilitators or mixed (i.e., both) and aligned with 13 of the 14 TDF domains, plus two additional domains: 'carer perspectives on the CPT intervention' and 'patient/carer characteristics'. Synthesized data revealed eight key theoretical domains: Environmental context and resources; Social influences; Beliefs about consequences; Skills; Memory, attention and decision-making; Knowledge; Beliefs about capabilities; and Reinforcement. Within each domain, the research team identified common categories and developed illustrative examples of theoretically informed implementation strategies. CONCLUSIONS & IMPLICATIONS: This systematic review and theory-informed synthesis of previously reported CPT implementation factors enabled the identification of key barriers to SLTs delivering this best practice. This led to proposed implementation strategies that should be validated, refined and evaluated in future research involving stakeholders who have contextual understanding of implementing CPT. WHAT THIS PAPER ADDS: What is already known on the subject CPT of familiar partners of PWA is an effective intervention that is inconsistently used in clinical settings. Factors influencing CPT implementation have previously been identified, but using disparate approaches and frameworks. A synthesis of these factors articulated around a common framework is currently not available. What this paper adds to existing knowledge This paper provides a theory-informed synthesis of previously reported barriers and facilitators to SLTs implementing CPT with familiar partners of PWA. It highlights key factors influencing the uptake of this best practice and includes suggestion of implementation strategies to address them. What are the potential or actual clinical implications of this work? The key influencing factors and proposed implementation strategies reported in this paper may support stakeholders in the future design of tailored and theoretically informed implementation strategies aiming to improve the delivery of familiar CPT in their setting.