As we have discussed, it's important that partners are in agreement about how to define success for a given PPP project. But measuring that success-determining the metrics by which a successful PPP will be distinguished from an unsuccessful one-is a challenge in and of itself. Metrics that are too vague or insufficiently quantifiable create uncertainty in the partnership. This uncertainty can lead to sub-optimization, or even the outright failure of the partnership. What kinds of metrics can be used to define success or failure?