Personal Interest (PI) is a basic concept. It is a multifaceted and multilevel psychological formation — a kind of “entelechy” — that is an integral part of any living organism, starting from the cell, system of cells and up to the most highly organized organisms and systems, which are formed by expansion into the external environment and interaction with it.

We introduce the concept of PI due to the presence of selectivity of connetions to the external environment, as well as situative (contextual) information analysis performed by all the living systems (LS) and their derivatives — even on the level of a cell. These are fundamental and indispensable properties of the PI.