Evolutionary Trends in Star Formation

Over the past 20 years, the Galactic plane has been surveyed at high resolution at wavelengths from 1 micron through to 20 cm. The combination of these surveys have produced large samples of deeply embedded young stars located across the Galactic disc. These continuum surveys are complemented by spectral line surveys of thermal, radio recombination, and molecular maser (OH, H2O, CH3OH) lines. The identified sources cover the whole range of evolutionary stages in the star formation process. This information has been used to calculate the physical properties of these stages and evaluate the impact of environment and location on star formation across the Galactic disc. This review provides an overview of some of the most significant studies in recent years and discusses how the evolutionary sequence has been used to investigate the correlation of other star formation tracers and maser associations.