The main subject of this paper is the classification and identification of observables for present and future grids. In order to make an inventory of present and potentially new observables, a systematic classification and identification of observables for future grids is conducted. After first introducing some fundamental definitions for observables, observables are further classified by the characteristic time scale where they are used in the physical power system. For actual use in control loops, observables must be part of so-called 'Control Triples' consisting of control aim, observable, and system input signal. A survey of existing and potential Control Triples was conducted among partners in the European ELECTRA project, resulting in a spreadsheet inventory. The main findings are presented and a few major observability needs for realising the so-called 'vertical integration' of control schemes reinforced by 'horizontal integration' of distributed control schemes in the future grid. © 2015 IEEE.