1. Introduction

2. Determination of the IBL from Galaxy Photon Emissivities
2.1. Luminosity Densities
2.2. Average Colors
2.3. Photon Density Calculations

3. Determination of the Optical Depth to γ-rays and resulting γ-ray Horizon

4. Application of our results to PKS 1424+240

5. Comparison with Other Results

6. Conclusions