Background: Advance care planning comprises discussions about an individual?s wishes for future care while they have capacity. Aim: To explore professionals? experiences on the implementation of advance care planning in two areas of clinical care, dementia and palliative care. Design: Qualitative study, focus groups and individual interviews. Setting: North East of England. Sample: Ninety-five participants from one Primary Care Trust, two acute National Health Service Hospital Trusts, one Ambulance Trust, one Local Authority and voluntary organisations and the legal sector. Results: Fourteen focus groups and 18 interviews were held with 95 participants. While professionals agreed that advance care planning was a good idea in theory, implementation in practice presented them with significant challenges. The majority expressed uncertainty over the general value of advance care planning, whether current service provision could meet patient wishes, their individual roles and responsibilities and which aspects of advance care planning were legally binding; the array of different advance care planning forms and documentation available added to the confusion. In dementia care, the timing of when to initiate advance care planning discussions was an added challenge. Conclusions: This study has identified the professional, organisational and legal factors that influence advance care planning implementation; professional training should target these specific areas. There is an urgent need for standardisation of advance care planning documentation. Greater clarity is also required on the roles and responsibilities of different professional groups. More complex aspects of advance care planning may be better carried out by those with specialist skills and experience than by generalists caring for a wide range of patient groups with different disease trajectories.