Microwave spectroscopy played a crucial role in structure determination of molecules in the gas phase during the 1950s - 1970s. As the number of molecules in the gas phase with a permanent dipole moment, a requirement for molecules to absorb/emit microwave radiation, is small, the field of microwave spectroscopy was almost disappearing. Very few laboratories in India which had established microwave spectroscopy and they were closed. Around 1980, Bill Flygare combined the cavity Fourier transform microwave spectrometer with a pulsed nozzle and this revolutionized the field of microwave spectroscopy. Weakly bound complexes that exist at very low temperature, 2-3 K could be investigated. Our laboratory at the Indian Institute of Science built a modern version of this spectrometer in 2000. Detailed investigations on weakly bound complexes having H2O and H2S, led us to a thorough molecular level understanding of intermolecular interactions. This helped us lead an international task group formed by IUPAC to redefine 'hydrogen bonding' , a concept used by chemists and biologists for close to a century. Hydrogen bonding is crucial in water and DNA, both molecules of life. During the last decade, a chirped pulse microwave spectrometer has been developed, which has led to another revolution in microwave spectroscopy. Our laboratory is planning to build a chirped pulse spectrometer and some preliminary results will be given.