In the past years we have made great efforts to reduce the statis-tical and systematic uncertainties in stellar parameter and chemical abundance determinations of early B-type stars. Both the construction of robust model atoms for non-LTE line-formation calculations and a novel self-consistent spec-tral analysis methodology were decisive to achieve results of unprecedented pre-cision. They were extensively tested and applied to high-quality spectra of stars from OB associations and the field in the solar neighborhood, covering a broad parameter range. Initially, most lines of hydrogen, helium and carbon in the optical/near-IR spectral range were reproduced simultaneously in a consistent way for the first time, improving drastically on the accuracy of results in pub-lished work. By taking additional ionization equilibria of oxygen, neon. silicon, and iron into account, uncertainties as low as ～1% in effective temperature, ～10% in surface gravity and ～20% in elemental abundances are achieved—compared to ～5-10%, ～25% and a factor ～2-3 using standard methods. Several sources of systematic errors have been identified by comparison of our analysis methods for early B-type stars with previously used standard techniques, e.g., the VLT-FLAMES survey of massive stars. Improvements in automatic analyses are strongly recommended for meaningful comparisons of spectroscopic stellar parameters and chemical abundances ("observational con-straints") with predictions of stellar and galactic chemical evolution models.
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