"Version: 202112"--Title page verso.Includes bibliographical references.1. Introduction -- 1.1. Why does habitability matter? -- 1.2. Defining habitability -- 1.3. The terrestrial planet demographic2. Habitability factors -- 2.1. An intricate puzzle -- 2.2. Stellar astrophysics -- 2.3. Planetary properties -- 2.4. The planetary system -- 2.5. A statistical approach3. Nature's fusion reactors --…