Lecture notes from the Summer School "Infrared Astronomy: Today and Tomorrow," held in Les Houches, August 1998. Editors F. Casoli and J. Lequeux.

Table of Contents

• INTRODUCTION
• THE STUDY OF NORMAL GALAXIES
• GALAXIES IN THE INFRARED: THE IRAS ERA
• Basic Parameters and Statistics
• Infrared Luminosity
• The Infrared-to-Blue Ratio
• IRAS Colors
• Other Estimators
• Correlations
• The Infrared-Radio Connection
• The ``Two-Component Model''
• ISO RESHAPES THE DUST CONTINUUM
• ISO Surveys of Galaxies
• Mid-Infrared Spectra
• The Aromatic Features
• The Mid-Infrared Continuum
• High-Redshift Applications
• Exceptions
• The ISO-IRAS Color Diagram
• The Global Infrared Spectrum
• A Mid-Infrared Look Within Galaxies
• A WALK IN THE LINE FOREST
• Molecular Lines
• Fine-Structure Lines
• Interpreting the PDR Lines
• MORE STUDIES
• TOMORROW'S INFRARED GALAXIES
• Challenges and Prospects
• Suggestions
• CONCLUSION
• REFERENCES