1 INTRODUCTION  
2 IDENTIFYING THE OPTICAL COUNTERPARTS OF AT20G SOURCES  
3 FINDING REDSHIFTS  
3.1 Searching the 6dF Galaxy Survey  
3.2 Searching the Literature  
3.3 Additional Redshifts  
3.4 Redshift Completeness  
4 SPECTRAL CLASSIFICATIONS  
4.1 The AT20G Spectroscopic Sample  
4.2 SuperCOSMOS Classifications vs. Spectral Classifications  
5 THE AT20G–OPTICAL CATALOGUE  
5.1 K-corrections  
6 RESULTS  
6.1 Optical Properties of AT20G Sources  
6.2 Compact vs. Extended Radio Sources  
6.3 Flat vs. Steep-Spectrum Radio Sources  
6.4 Accretion Mode vs. Radio Properties  
6.5 Optical vs. Radio Luminosities  
7 COMPARISON WITH S-CUBED 18 GHZ SELECTED SAMPLE  
8 SUMMARY