The interstellar medium (ISM) is the vast space between stars in a galaxy, primarily consisting of gas (mostly hydrogen and helium) and dust particles. Researchers study the ISM to understand its properties, composition, and role in star formation, planetary systems, and galaxy evolution. The ISM is also crucial for the process of interstellar dust grain nucleation and growth, and is responsible for cooling interstellar gas through molecular line emissions. Various observational techniques, such as radio astronomy and infrared spectroscopy, are used to study the ISM and gain insights into its physical and chemical properties. Understanding the ISM is essential for building a complete picture of the universe and its complex dynamics.