Some solutions, some problems, and some questions

This is a slightly expanded written version of a plenary lecture given at the 20th IEEE Conference on Decision and Control, December 1981, San Diego, CA. This talk is intended to help spark discussion among researchers in decision, control and estimation about the status of research in the field and of promising new directions for research. One such direction, model-based signal processing, is treated in some depth together with an example, an object detection and estimation approach to tomographic reconstruction. Several additional topics are treated through the posing of questions which hopefully will provoke responses.