Perhaps one of the most extreme environments is that of interstellar space. Here material exists in a high vacuum with temperatures ranging from very cold to exceptionally hot, bombarded by intense ultraviolet radiation. Despite these conditions, observations have shown that molecular matter is found throughout our Galaxy. Most known interstellar molecules are small ( < 10 atoms) gas-phase species. Many are “non-terrestrial” radicals and ions, such as C4H, c-C3H2, and HCO+ while others are quite common to Earth (CH3OH, NH3, H2O). Some are rare metal-bearing compounds with iron, aluminum, magnesium, and even vanadium. Recently, fullerene species have been identified in interstellar gas: C60 and C70. At the same time, the solid-state is well-represented by small, 1-10 microns grains, thought to be silicate or carbonaceous in composition. An overview of these molecular materials will be discussed, the links between various phases, and the possibilities for other forms of matter, including nanotubes.