My aim is to write a book in theoretical psychology, which I perceive as a subfield of theoretical biology. More particularly, the theme which I will focus on is the nature of mind and agency. I take the mind to be the control system of certain species of organisms (probably, the Vertebrates) in their interaction with their subjective environment. The environment is subjective in at least two senses. First, because the dynamics of the external world which are relevant to the organism are constructed by the control system itself, whose functioning is grounded in the particular biology and psychology of each particular species of organisms. The subjective environments of, say, a bat and of a human are not one and the same; while both have to be compatible with "the real world," they cannot, need not, and do not faithfully mirror it. It is the functioning of the control systems, that is, its internal dynamics, that generates what external dynamics the organism is capable of constructing and acting upon. The second reason why the environment is subjective is that the mind is a subjective entity. I equate terms like mind, representation, consciousness, meaning, semantics, and Intentionality. An agent's subjective environment may thus be viewed as a landscape of dynamic meanings (that is, roughly, affordances) whose flow constitutes the agent's situation. An agent is an Intentional, conscious organism who lives in a situation, (that is, a subjective, open, and changeable representation of the world) and strives continuously to make it more to its liking. The book I plan to write will outline, discuss, and defend both the foundations of such a view (which is rather distant from what is current wisdom in mainstream psychology and cognitive science) and some of its consequences on how agency and social agency (including communication) can and should be conceived of.