1. Introduction

2. An empirical metallicity scale
2.1. The calibrators

3. The sample of M31 globular clusters

4. Comparisons with other sets of metallicities
4.1. Comparison with [Fe/H] from empirical calibrations
4.2. Comparison with [Fe/H] from SED fitting
4.3. Comparison with [Fe/H] from CMDs

5. Discussion and Conclusions
5.1. Metallicity distribution
5.2. Metallicity and kinematics