"Stage-gate" is actually a registered trademarked process from a company called Stage-Gate Inc. However, the term is often used for any product development process that goes through a number of development stages with approval steps (aka "gates”). A project can not pass through the gate unless it meets a certain level of approval or completeness.

Regardless of the project management methodology that is used, product managers are the messenger of the market, and are responsible for the business case and the clearly articulated market requirements for the product. Using Stage-Gate's terms, product managers would be closely involved with Discovery and the "Idea Screen" - the first gate - bringing concepts to the business. In our training, we teach this as market problem and market segment identification. Stage 1 is called Scoping, where the business evaluates projects at a high level to narrow the number of projects that are being proposed. As "president of the product," product managers must be involved to deliver the market facts as to why certain products are more or less important to the business, which represents the second gate.

Product managers are accountable for the Business Case, the next stage. The next gate is the hand-off to development. This is where product managers communicate clearly to development the prioritized market problems that need to be solved, key user personas, use scenarios, and requirements. After this gate, product managers need to remain informed about the status of the project, and to represent the market in case requirements or conditions change, or if product requirements need to be re-prioritized or clarified during the development stage. However, we should leave the development and testing stages and gates to the development organization.

Depending on your organizational structure, product managers may or may not own the product launch, the last gate. Undoubtedly, we own components of the launch, such as product positioning and sales tools. Launch is often the responsibility of product marketing.

Product managers should also be involved in the last stage, post-launch reviews. Many companies leave this stage to project management or development. However, post-launch reviews should look at the entire process, from concept to market launch, so product managers can drive and own a large part of this stage.

There is an interesting article that you may want to look at that explains stage gate processes in the context of multiple, small, iterative projects. All of the points above still hold. Click Here for a link to the article.