2.1 Gain and Loss: Achieving Lasing2.2 The Gain Threshold Equation2.3 The Tale of Two Gains: g0 AND gth2.4 Application of gth: Determining g02.5 An Atomic View of Gain: Cross-Section2.6 Applications of the Gain Threshold Equation: Designing Laser Optics2.7 A Theoretical Prediction of Pumping Threshold