This white paper examines questions and related challenges that are needed to frame a discussion about the approach to interoperability that can help lead to an effective and sustainable smart grid. Industry thought leaders were interviewed to provide insight into the issues surrounding interoperability. These individuals represent the spectrum of smart grid stakeholders, from regulators to technology experts, and were selected based on their experience and involvement with smart grid activities. Less formal discussions were held with other stakeholders involved in smart grid interoperability efforts to help develop and synthesize concepts and details. This input, combined with additional background research, led to the development of the themes presented. The white paper draws out and explains issues, develops insights regarding their relative importance, and provides recommendations to help achieve high interoperability.