Traditional software lifecycles put significant effort in analysis, design, and implementation before their results can be tested. The start of testing late in the lifecycle often uncovers flaws from these early phases that require significant rework of analysis and design. We describe a software lifecycle where each phase of development is followed by an execution test of the results of that phase. This lifecycle is progressive in the sense that it does not require significant "backing up" to earlier phases of development. The use of this lifecycle requires tool support that is just now becoming available. We examine this lifecycle and its implications for embedded software development.