Massive Star Forming Regions: from diagnostic tools to derived properties

The current state-of-the-art of multi-wavelength diagnostic tools (evolutionary synthesis, photoionisation models) for massive star forming regions (HII regions, starbursts, etc.) and some of their input physics (especially model atmospheres) is reviewed. Analysis of stellar populations based on integrated spectra from both stellar features and nebular emission lines from the UV to IR are summarised. We stress the importance of “template” studies at various scales (from individual stars to well studied galaxies) and various wavelengths, to understand the processes operating in massive star forming regions and to reliably derive their properties.