This is an introduction to firm’s financial sustainability new ideas beyond the environmental sustainability concerns, based on a principle: balance and a method: interaction. It is specifically addressed to the interaction between the two kinds of financial policies: short-term financial policy (dynamic factor) and long-term financial policy (static factor), as it happens on the universe and wealth production. And when the firms target is to achieve a financial sustainability level, growth is not so important and so necessary as in any other financial situation.