1. INTRODUCTION  
2. SAMPLE DEFINITION AND OBSERVATIONS  
3. BOLOMETRIC LUMINOSITIES AND TEMPERATURES  
3.1. The BLT Diagram  
3.2. Dependence of the BLT Diagram on Region  
3.3. Luminosity Outbursts  
3.4. Effect of Incompleteness and Extinction  
4. UNDERSTANDING PROTOSTELLAR EVOLUTION VIA SED MODELING  
4.1. Model-based Masses as an Envelope Diagnostic  
4.2. Model-based Total Luminosities  
4.3. Total Luminosity versus Envelope Mass  
5. ANALYSIS OF LUMINOSITY AND ENVELOPE EVOLUTION  
5.1. The Flat Distribution of Envelope Mass  
5.2. Decreasing Luminosities with Evolution  
5.3. Scatter in Luminosities: Episodic Accretion  
5.4. Variation as a Function of Environment: Changing Star-Formation Rates?  
6. CONCLUSIONS