Current jet control goals are mixing enhancement, flow tailoring for high-performance aerodynamic applications, and noise reduction. The four projects in this group were motivated by these broad objectives. The first project took steps toward developing real-time closed-loop controls for both mixing enhancement and flow tailoring applications. A necessary element of this approach is a model for the jet which is accurate yet simple enough to be able to predict the jet's response to actuation in real time. Alan Cain of the Boeing Company was assisted by Bewley, Freund, and Colonius in developing such a model. Locally unstable linear modes were used to compute shear stresses which were then used in a streamwise evolution equation for the shear layer thickness. The novel aspect of this work was the use of analytically tractable approximate mean flow profiles which provided closed-form analytical expressions for the stability problem. Because of this, the entire model can, once optimized, be evaluated rapidly enough for a real-time application. Koumoutsakos, Freund, and Parekh tested evolution algorithms, which are motivated by the well-known ``mutate and compete'' principles that govern the evolution of biological systems, as a tool for optimizing nozzle actuation for jet mixing enhancement. An important advantage of this type of algorithm over many other approaches is its portability. In this project, the same program subroutines were used to optimize actuation in both a low Reynolds number DNS and a vortex method simulation. Starting from a random initial guess for the actuation parameters in the DNS, the evolution strategy ``found'' parameters that had previously been shown to be highly effective in both laboratory experiments and in simulations. In the vortex method simulation, having also started from a random initial guess, the evolution algorithm found parameters that produced the well-known bifurcating jet flow. Surprisingly, the algorithm also found a previously unknown set of parameters that added a kink to the bifurcating flow pattern which further increased the spreading rate of the jet. It is well known that the downstream evolution of a jet is closely tied to large turbulent structures in the flow. In an effort to understand these better with an eventual goal of using them to improve controls, a study of the large scale dynamics of jets was conducted by Danaila and Beorsma using a spherical coordinates DNS code. Combinations of axisymmetric and n = 1 modes were excited in the jet causing pulsing, flapping, and bifurcating jet flows. These results were analyzed in detail, and a new mechanism leading to jet bifurcation was proposed. This is of particular interest because bifurcation can greatly enhance the spreading of the jet and thereby increase its mixing. Using an existing DNS database of a Mach 1.92 jet, Colonius, Mohseni, Freund, Lele, and Moin undertook an effort to study the mechanisms of jet noise. The eventual goal of this effort is to develop new models and test existing models that could be incorporated into a control scheme. An important result of this study was the successful computation of the Lighthill acoustic source and verification of its ability to produce the correct acoustic radiation. In addition, an analysis based upon the linear adjoint equations was completed, which will provide a means for utilizing the available DNS databases to evaluate linear models for noise.