Of all the agile software development methodologies, outside–in software development takes a different approach to optimizing the software development process. Unlike other approaches, outside–in development focuses on satisfying the needs of stakeholders. The underlying theory behind outside–in software is that to create successful software, you must have a clear understanding of the goals and motivations of your stakeholders. Your ultimate goal is to produce software that is highly consumable and meets/exceeds the needs of your client.
Outside–in software development is meant to primarily supplement your existing software development methodology. While it does ideally work in more agile environments, it is possible to fit outside-in development into waterfall-based or six sigma methodologies. Outside–in software development is not a catchall solution, but a way to better your existing methodology.