As Agile practices move further toward mainstream adoption, we see significant benefits from the adoption of Lean software development practices as well. These practices have their roots in the Toyota Production System and complement much of our understanding of Agile software development to date. One topic that Lean has also given us greater insight into is that of set-based design. Set-based design leads us to implement similar solutions at the same time while the cost of doing so is constrained. This leads us into the area of emergent design and the ability to let experience shape our design decisions and defer key decisions until the last responsible moment.