Astrochemistry draws its inspiration, language, fascination, beauty, elegance and confusion from many different disciplines: starting with astronomy, passing through physical chemistry and ending with the new ideas of astrobiology. It is this breadth of fascination that I have attempted to capture in Astrochemistry: from Astronomy to Astrobiology. Choosing such a broad subject comes with the serious problem of how to limit the discussion of the details to allow an appreciation of the whole. I could have written an entire book on molecular astrophysics, looking at what molecules are doing in the various environments of space. I could have looked simply at the wonders of planetary chemistry, concentrating on the solar system or even just one planet such as Jupiter. Why does it have a giant red spot? Instead, I have chosen to apply a more general boundary condition for the book taking in all of the subjects but focused on the theme of "The Origin of Life". The book I have tried to constrain the wonders of imagination inspired by the subject by using simple calculations. Can all of the water on the Earth have been delivered by comets: if so, how many comets? How do I use molecular spectroscopy to work out what is happening in a giant molecular cloud? Calculations form part of the big hard-sell for astrochemistry and they provide a powerful control against myth. I have aimed the book at second-year undergraduates who have had some exposure to quantum mechanics, kinetics, thermodynamics and mathematics but the book could easily be adapted as an introduction to all of these areas for a minor course in chemistry to stand alone.