Astrochemistry --- also called molecular astrophysics, studies the chemical aspect of astrophysics.  Over the years more than 200 molecules have been detected in space, most of which are organic.  Understanding the origin of these molecules is one of the major tasks of astrochemical study, and helps to infer the physical state of interstellar medium.  In this talk I will review some of the important topics of astrochemistry, including its use as a diagnostic tool, and how they could be related with the origin of our solar system.