Abstract. The use of Virtual Environments as a user interface is essential for certain types of applications, both in education and entertainment. These worlds are even more attractive for the user when they are neither static nor pre-scripted, but have dynamic characteristics and are populated by autonomous entities, also called virtual agents. There has been a lot of research concerning visualization, animation and behavior of virtual agents, but there are no generic architectures, methodologies and tools for the development of intelligent virtual environments, i.e. 3D environments with autonomous virtual agents. In this paper, we present SimHuman, a tool for the construction of virtual worlds with autonomous entities, targeted for a specific group of applications, such as simple simulation systems, virtual environments, educational applications, multimedia presentations, etc. It consists of a programming library and two utilities and it is highly dynamic and configurable, as it is not based on fixed scenes and models. It has embedded characteristics such as Inverse Kinematics, Physically Based Modeling, Collision Detection and Response, and Vision. SimHuman incorporates some important features for designing and building virtual environments and turns out to be an effective tool for interactive 3D applications with virtual agents.