Venus today presents a type example of how habitability can fail to persist on a planet: rocky and to a first order overwhelmingly Earth-like, but with a climate profoundly hostile to life’s complex molecular machinery. But, was it always like this and will we know a Venus from an Earth when we see one elsewhere in the galaxy? This talk investigates what evidence there may be for Venus’s past climate state, and relates this to the frontier of our search for habitable conditions on exoplanets.