1. Overview. 1.1. Introduction. 1.2. Cometary Panspermia. 1.3. History of Panspermia. 1.4. The ultraviolet problem. 1.5. Resilience of bacteria. 1.6. Extremophiles. 1.7. The discovery of organics in cosmic dust. 1.8. Comets. 1.9. The origin of life. 1.10. Modern advances. 1.11. Protoplanetary nebulae and extra-solar planetary systems. 1.12. Habitable zone -- 2. Cosmic dust and life. 2.1. Introduction. 2.2. Constraints on composition. 2.3. Extinction by spherical particles. 2.4. The interstellar extinction and bacterial dust. 2.5. Infrared evidence. 2.6. Comet dust and biomaterial. 2.7. The identification of PAH and biological aromatics. 2.8. Other spectral features. 2.9. Fluorescence. 2.10. The origin of organic molecules in space. 2.11. Direct analysis of comet dust. 2.12. Capture of comet dust in the stratosphere -- 3. The origin of comets. 3.1. The galactic disc. 3.2. The formation of stars. 3.3. Planet formation. 3.4. The formation of comets -- 4. Comets in the galactic environment. 4.1. The mechanism of lithopanspermia. 4.2. The formation sites of comets. 4.3. The sun's orbit in the galaxy. 4.4. The impact cratering record -- 5. Dark comets : a link to Panspermia. 5.2. The impact hazard and the Panspermia connection -- 6. Expulsion of microbes from the solar system. 6.1. Introduction. 6.2. Expectations from impact cratering mechanisms. 6.3. Mechanisms for ejection and fragmentation of boulders. 6.4. [symbol]-meteoroids. 6.5. Protective shielding in small [symbol]-meteoroids. 6.6. Carbonisation of the surface layers of grains. 6.7. Radiation pressure effects. 6.8. Surviving the hazards of galactic cosmic rays. 6.9. How comets distribute life. 6.10. Dispersal of life by impacts -- 7. Liquid water in comets. 7.1. Introduction. 7.2. Primordial melting. 7.3. Evidence of present-day melting. 7.4. Results from Deep Impact. 7.5. Frozen lake surfaces. 7.6. Microbial fossils in carbonaceous meteorites -- 8. Origin of life. 8.1. Preamble 183. 8.2. Cometary interiors as incubators of early life. 8.3. Comparison with a terrestrial origin of life -- 9. Expanding horizons of life.