In this chapter we assume the perspective of environmentally conscious investors. We hold that the latter are interested in both the objective determinants and the subjective factors that determine if and to what extent owners of an externalities producing technology incorporate these externalities into their production functions. We use public value theory as concept that explains the normatively determined inclusion of externalities into a firm's production function as a result of changing consumer preferences and dynamic legislative environments. We propose that environmentally conscious investing can be compared to buying a put option on public value risks and describe the mechanics of this option.