The development of photoelectron spectroscopy since the early days of the technique is discussed. The focus is on the interaction between instrumental development and scientific achievements. In particular the opportunities provided by the increasingly brilliant synchrotron radiation sources are discussed. The contribution is focused on core level studies. The recent development is demonstrated by using selected examples obtained at today's most advanced synchrotron radiation facilities. The spectral resolution and intensity that can be reached at these facilities reveal new effects and provide detailed information on the investigated systems. The examples are mainly taken from studies of atoms and molecules where different effects can be most accurately identified and separated.