The provision of professional pharmacy services has been heralded as the professional and the economic future of pharmacy. There are different phases involved in a service creation including service design, impact evaluation, implementation and sustainability. The two first phases have been subject to extensive research. In the last years the principles of Implementation science have been applied in pharmacy to study the initial uptake and integration of evidence-based services into routine practice. However, little attention has been paid to the sustainability of those services, during which there is a continued use of the service previously implemented to achieve and sustain long-term outcomes. The objective of this commentary is to describe the differences and common characteristics between the implementation and the sustainability phase and to propose a definition for pharmacy. A literature search was performed. Four critical elements were identified: 1. The aim of the implementation phase is to incorporate new services into practice, the sustainability phase's aim is to make the services routine to achieve and sustain long-term benefits 2. At the implementation phase planned activities are used as a process to integrate the new service, at the sustainability phase there is a continuous improvement of the service 3. The implementation phase occurs during the period of time between the adoption of a service and its integration. Some authors suggest the sustainability phase is a concomitant phase with the implementation phase and others suggest it is independent 4. There is a lack of consensus regarding the duration of each phase. The following definition of sustainability for pharmacy services is proposed: “Sustainability is a phase in the process of a professional pharmacy service, in which the service previously integrated into practice during the implementation phase is routinized and institutionalized over time to achieve and sustain the expected service outcomes”. An agreement on a definition will facilitate an understanding of when the profession has reached this ultimate goal.