Nebular emission lines are a powerful diagnostic tool for tracing the chemical evolution in star-forming galaxies (SFGs) across cosmic time. Due to their proximity, SGFs are ideal for studying the physical properties, stellar population, and nebular gas in much more detail. The COS Legacy Spectroscopy SurveY (CLASSY) is a treasury survey that

H II regions, ionized nebulae associated to massive star formation, exhibit a wealth of emission lines that are the fundamental basis for estimating the chemical composition of the Universe. For more than 80 years, a discrepancy of a factor of around two between heavy-element abundances derived with collisional excited lines (CELs) and the weaker

In this seminar I will focus on how the avalanche of new data changes our views on how our Galaxy formed and evolved. Precise astrometric, spectroscopic, photometric and asteroseismic data can be combined to pin down different processes that have shaped the Milky Way. This data will be discussed and illustrated with examples of what is possible to