The development, integration, and testing of a general-purpose "computational steering" software library with a three-dimensional Navier-Stokes flow solver is described. For this purpose, the portable object-oriented scientific steering environment (called POSSE) library was used. This library can be coupled to any C/C++ simulation code. The paper illustrates how to integrate computational steering into a code, how to monitor the solution while it is being computed, and how to adjust the parameters of the algorithm and simulation during execution. The simulations typically run on a parallel computer, whereas the visualization is performed both on the parallel machine and on other computers through a client/server approach. In addition, the visualizations can be displayed using virtual reality (stereographics) facilities to better understand the three-dimensional nature of the flowfields. A key advantage of our interactive CFD system is its scalability. For large-scale simulations it is often not possible to postprocess the entire flowfield on a single computer due to memory and speed constraints. Therefore, scalable interactive computational steering and monitoring systems are essential. Example applications are presented including flow over a helicopter fuselage, a helicopter rotor, a ship airwake, and a landing gear. The advantages of using object-oriented programming are also discussed. Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.