About 5000 exoplanets have been confirmed, and the number is still increasing rapidly. Discovering planets itself is insufficient, however, unless we also know which of them are potentially habitable: Do any of these planets have conditions that would support life? What factors favor the building and maintenance of a temperate environment for life? In this talk, I will present how to define habitable zone around stars and how to estimate the habitable zone based on 1D and 3D climate models. I will review recent advances, such as limited CO2 cycles, habitable H2 worlds, and the effects of clouds and sea-ice motion. Identifing which planets are potentially habitable or unhabitable is critical for follow-up atmospheric characterizations and biosignature detections.