Over the years, many different agent programming languages have been proposed. In this paper, we propose a concept called Agent Programs using which, the way an agent should act in various situations can be declaratively specified by the creator of that agent. Agent Programs may be built on top of arbitrary pieces of software code and may be used to specify what an agent is obliged to do, what an agent may do, and what an agent may not do. In this paper, we define several successively more sophisticated and epistemically satisfying declarative semantics for agent programs, and study the computation price to be paid (in terms of complexity) for such epistemic desiderata. We further show that agent programs cleanly extend well understood semantics for logic programs, and thus are clearly linked to existing results on logic programming and nonmonotonic reasoning. Last, but not least, we have built a simulation of a Supply Chain application in terms of our theory, building on top of commercial software systems such as Microsoft Access and ESRI's Map Object. (Also cross-referenced as UMIACS-TR-98-15)