The future is open, therefore it is impossible to predict correctly what is to come. Nevertheless, we have expectations about the future because man has got the experience that substantial trends, which have their origin in the past, will continue. This means, from the view of natural sciences, the fundamental laws of physics and chemistry set a frame also for the time to come. First of all, the conservation theorems and the principle ot dissipation of energy and matter set boundaries to our activities. From this assertion the existence of quantitative limits of growth and limits of population capacity on earth is deduced. These limits are dynamic quantities whish depend on many variables, particularly on human behaviour. Within the given boundaries it is possible to establish a sustainable society Man himself is responsible for his future.