In the paper a multi-agent technology based on integration of the object- oriented approach and constraint programming is proposed. The key notion of this technology is an ’’active object” that has three specific features. First, an active object has the ability to change its state based on the analysis of the states of other ’’visible” objects. Second, the interaction of active objects is asynchronous and controlled by events rather than messages. Third, the behaviour of an active object, that is, its transitions from one state to another, is described by constraints rather than methods. In addition, we propose a new solution to the problem of integrating imperative programming with constraint programming. In the technology of active objects, it is the constraint paradigm which plays the leading role. It is extended by the capability of simulating sequential processes, using the mechanism of conditional constraints and the semantics of the tick-by-tick computations.