Background: Advance care planning (ACP) is thought to enhance patient autonomy and improve end-of-life care. However, there is evidence that when patients engage in ACP, the resultant plans are often not implemented. This has been attributed to either nonadherence by health professionals or inadequacies in ACP such as inaccessibility of the plans, plans providing ambiguous or conflicting instructions, and inappropriate focus on the completion of documents rather than communication. However, it is not known whether these postulated reasons are consistent with the experiences and views of health care professionals providing end-of-life care in the community. Objective: Our aim was to explore the perspectives of general practitioners (GPs) on factors influencing the implementation of ACPs. Methods: We conducted semi-structured, open-ended interviews of a purposive sample of 17 Australian GPs. Interview transcripts were analysed using constructionist grounded theory utilizing NVivo 9 software. Results: Factors that were considered to have an important influence on the implementation of ACPs include: ACP factors such as form, legal standing, accessibility, clarity, currency, and specificity; illness factors such as quality of life, function, diagnosis, prognosis, and prognostic certainty; family factors such as family attitudes to ACP and different conceptualizations on whether care is provided to individuals or to a family unit; and organizational and care setting factors such as health care facility's attitudes and policies in relation to end-of-life care. Conclusions: Problems in implementation of ACPs are multifactorial and not necessarily due to deliberate nonadherence by health professionals. Potential solutions to improve the clinical impact of ACP are discussed.