Implementation of innovations – social, technical and scientific – often fails. Implementation science is the multi-disciplinary field that addresses how implementation can succeed. This article summarizes some basic premises in four questions: 1) Is the innovation the best solution to an important problem? 2) What behavior changes does the innovation require? 3) What strategies are needed to make the changes possible, probable and lasting? and 4) How is the innovation used? In this, implementation is positioned as a way to create a fit between the innovation and the context. It highlights that the end result depends on the innovation, the context and the implementation strategies together.