Like most other types of instrumentation systems, flight test instrumentation is not produced in series; its development is a one-time achievement by a test department. With the introduction of powerful digital computers, instrumentation systems have included data analysis tasks that were previously limited to post-experiment processing. However, the resulting integrated systems are hard to maintain in the traditional environment of instrumentation development. Software-Enabled Modular Instrumentation Systems describes the theory and praxis of a new methodology to analyze, design, implement, and validate a digital signal processing system for test and evaluation applications in the information age. Based on life cycle concepts from software engineering, this dissertation presents an object-oriented approach that allows to combine proprietary and off-the-shelf components in a way that reusability of the elements and extensibility of the application are ensured. The methodology covers all phases of test and evaluation: desktop simulation, hardware- and pilot-in-the-loop simulation, flight test, and post-experiment data analysis. Moreover, optimum reusability of the components is ensured not only through the phases of the project, but also from one test program to the next. The methodology thus results in reduced system development time and cost, and improved system reliability.