1. INTRODUCTION

2. THE AGN CONTRIBUTION IN LOCAL ULIRGS AND LIRGS
2.1. Sample selection and data reduction
2.2. Distribution of the AGN contribution
2.3. Simulating the distribution of the AGN contribution
2.4. Evolution with redshift

3. MODEL DESCRIPTION

4. RESULTS AND COMPARISONS WITH AVAILABLE SURVEYS
4.1. Pure starbursts SEDs
4.2. Adding the AGN contribution
4.3. Evolving the L-T relation
4.4. Evidence for a local "cold" population?

5. STAR FORMATION HISTORY

6. AGN CONTRIBUTION TO THE INFRARED EMISSION

7. OPEN ISSUES

8. PREDICTIONS FOR MULTIBAND HERSCHEL SURVEYS

9. CONCLUSIONS