With the increasing power dissipation increasing attention has been paid to the thermal issues in electronics design on system, board, package and chip level, including electrothermal simulation of even rather complex integrated circuits. Two distinct algorithmic directions can be distinguished in electro-thermal simulation: the simulator coupling and the simultaneous iteration or direct method. In our view the direct method is well suited for electro-thermal simulation of analog circuit blocks while simulator coupling can be used to implement logi-thermal simulation. In case of complex designs containing digital and analog blocks the two approaches can also be combined. Ideally thermal, electro-thermal and logithermal simulation of a circuit is performed already in the phase of conceptual design when only a rough idea exists about the final physical realization of the circuit. In any case, effect of the thermal boundary conditions of the die+package, cooling via the electrical connections to the die and the granularity of the simulation should be carefully considered.