The stage-gate model is a technique used in product development to manage the movement from one phase to the next. Each phase, or "stage", of the project, is separated by a figurative "gate" that prevents you from progressing onto the next milestone without sufficient pause for thought.
When using the stage-gate model in new product development, teams will typically progress through five phases: Discover, scoping, business plan concept, development, testing and validation, launch, and implementation. Each phase plays a crucial role in launching a successful product, and shortcuts throughout the process only serve to add risk and uncertainty to the development journey.
Before moving from one phase to another, teams should decide whether or not the project is ready to progress — avoiding concurrent development. When a gate is reached, teams will have to decide how to move forward, which can be answered by any of the following decisions:
Go. This means that the project is a success so far and you're ready to move on.
Kill. This means the project is not a success and should be abandoned.
Hold. This means the project is not strong enough to continue but not bad enough to be abandoned. Instead, it is put on hold until a better time, typically when more resources are available.
Recycle. This means the project has led to positive progress, but that you believe this progress should be invested in another project. Instead of moving forward, the project changes shape.