In-situ monitoring and advanced diagnostics to enable AM fundamental understanding (for example metrology). Additive manufacturing provides a fundamentally different way to build components, as opposed to subtractive manufacturing. Typically, in subtractive manufacturing, metrology is executed after all material is removed, as this is when the part receives its final shape. With AM, metrology can occur during the process and corrective actions can be taken in-situ. It is expected that in-process metrology will not provide a binary (go/no-go) result, but a probabilistic result (quantifying quality/conformance uncertainty). Thus, the concept of metrology for AM will be interpreted and represented differently than classical metrology. Furthermore, AM processes offer the opportunity to quantify errors and correct them in-process by incorporating sensors other than dimensional, resulting in significantly different closed-loop process control systems. AM enables the manufacture of multi-material, and functionally graded material components. Such a capability will require a new set of in process sensor tools to validate material quality, composition and key performance parameters.