1. INTRODUCTION

2. SAMPLE DEFINITION
2.1. SDSS-RM quasars
2.2. SDSS-I/II quasars

4. OBSERVED DISTRIBUTION OF ΔM

5. THE STRUCTURE FUNCTION: VARIABILITY AS A FUNCTION OF TIME SEPARATION
5.1. Definitions
5.2. The Damped Random-Walk Model

6. THE STRUCTURE FUNCTIONS OF CONTINUUM EMISSION
6.1. The 3000 Å Continuum
6.2. The 5100 Å Continuum

7. STRUCTURE FUNCTIONS OF EMISSION LINES
7.1. Mg II
7.2. H β

8. IMPLICATIONS FOR REVERBERATION-MAPPING PROJECTS

9. SUMMARY