The ever-increasing power of computers and hardware rendering systems has, to date, primarily motivated the creation of visually rich and perceptually realistic virtual environment (VE) applications. Comparatively very little effort has been expended on the user interaction components of VEs. As a result, VE user interfaces are often poorly designed and are rarely evaluated with users. Although usability engineering is a newly emerging facet of VE development, user-centered design and evaluation in VEs as a practice still lags far behind what is needed. In this article we present a structured, iterative methodology for the user-centered design and evaluation of VE user interaction. Figure 1 illustrates our basic technique: we recommend performing (1) user task analysis, followed by (2) expert guidelines-based evaluation, followed by (3) formative user-centered evaluation, and finally by (4) summative comparative evaluation. In this article we first give some motivation and background for our methodology, and then we describe each of these techniques in some detail. We then discuss how we applied these techniques to a real-world battlefield visualization virtual environment, and finally discuss why this approach provides a cost-effective strategy for assessing and iteratively improving user interaction in VEs.