1 INTRODUCTION  
2 THE INFORMATION IN GALAXY SURVEYS  
2.1 Optimal estimators and the Fisher matrix  
2.2 Single-species Fisher matrix  
2.3 Multi-tracer Fisher matrix  
3 THE OPTIMAL MULTI-TRACER QUADRATIC ESTIMATORS  
4 PROPERTIES AND RELATIONS OF THE MULTI-TRACER ESTIMATOR  
5 TESTING THE ESTIMATORS  
6 INCLUDING THE 1-HALO TERM  
7 CONCLUSIONS