Session presented at Lean Software and Systems Conference 2012 (LSSC12). As technology marches forward, system complexity continues to rise. Many of the most critical design decisions are made very early in projects, before the system designers can possibly know all that they need to know to make those decisions correctly. That inevitably results in what we call "loopbacks", where earlier decisions (that were thought to be final) must be re-made, resulting in a cascade of changes to portions of the design that were dependent on those earlier decisions. Avoiding that waste is a key driver of the Lean principle of delayed decision-making. However, putting that into action is not as simple as delaying decisions... it is often very hard to make progress on your design if you are waiting on various decisions to be made. This is where Set-Based Design comes to the rescue. Set-Based Design is often misrepresented as simply performing multiple Point-Based Designs in parallel so that you are more likely to have one good design. Rather, Set-Based Design will be described as a radical departure from traditional Point-Based Design, moving from the inefficient pattern of guess-then-test-to-validate to a highly efficient pattern of test-to-learn-then-design.