This booklet is part of an American Astronomical Society curriculum project designed to provide teaching materials to teachers of secondary school chemistry, physics, and earth science. The following topics are covered: the physical conditions in interstellar space in comparison with those of the earth, particularly in regard to gas density, temperature, and radiation; the concept of quantized molecular motion (electronic, vibrational, rotational), and the corresponding energy ranges of radiation; spectroscopic methods for identifying molecules in space; the organic nature of interstellar chemistry; and application of our knowledge of interstellar molecules to study the birth of stars, the structure and movement of our galaxy, the history of interstellar matter, and the origin of the universe and life. Each section is followed by questions and answers, and an appendix contains suggested student projects. Also included are a glossary of terms and suggested reference materials. (MH)