A fundamental book.
It represents the evolution from the original cybernetics of complex machines (observed systems) to the Second-Order Cybernetics, the one of the "observing systems", e.g. the human living systems.
Among the book's key concepts, the distinction between "banal and non-banal machines" and the fact that "human communication belongs more to the domain of ethics and love rather than of the ones of logic, mathematics or cybernetics".
Unmissable.