Aspects of this disclosure are directed to level-shifting approaches with communications between respective circuits. As may be implemented in accordance with one or more embodiments characterized herein, a voltage level of communications passed between respective circuits are selectively shifted. Where the respective circuits operate under respective power domains that are shifted in voltage range relative to one another, the voltage level of the communications is shifted. This approach may, for example, facilitate power-savings for stacked circuits in which a low-level voltage of one circuit is provided as a high-level voltage for another circuit. When the respective circuits operate under a common power domain, the communications are passed directly between the respective circuits (e.g., bypassing any level-shifting, and facilitating fast communication).