Mathematical modeling is a fundamental discipline within the design and development of modern electro-optical (EO) sensor systems. Modeling allows systems to be readily and cheaply evaluated before they are built and allows the assessment of modifications to existing products. The performance of systems can be gauged in different scenarios: ones that are either expensive to determine through trials, or else ones that are constrained through domestic or international sensitivities. Furthermore, modeling allows a designer to develop and test their own understanding as well as identifying critical trade-offs and risks. Modeling is, therefore, a powerful design technique that sits at the heart of modern EO sensor systems engineering.