The paper illustrates the role of quantitative spectroscopy for the diagnosis of fusion plasmas and the importance of extensive consistency checks. Four examples are given of recent spectroscopic observations which have triggered new approaches both to plasma modelling and atomic excitation processes. The examples highlight the role of passive charge exchange emission and its implication for plasma edge physics, non-thennal features in the HeII spectrum and temperature anisotropies observed in high power neutral beam heated plasmas, the importance of geometric mapping in an arbitrary magnetic configuration for the evaluation of line integrated spectra, and finally the complexity of atomic processes involved in the spectral analysis for helium transport studies.