We discuss statistical modeling of yields for products that are built layer-by-layer; typical examples include three-dimensional printing and semiconductor manufacturing. We focus on problems where product failure is primarily related to defects in various layers. Information available about the defects is typically incomplete, and there is a possibility of a product failing due to other causes. We describe a probabilistic approach to yield modeling, and discuss problems related to estimation, forecasting and yield management. This is joint work with Michael Baron and Asya Takken.