What is the difference between a PSD and AI?
PSD are bitmap based file formats that are generally a layered file that is proprietary to Adobe PhotoShop. PSDs enable the designer to change the colors of an image, and add or remove image layers. AI is a proprietary file format developed by Adobe Systems for representing single-page vector-based drawings which can be exported in either EPS or PDF formats. The .ai filename extension is used by Adobe Illustrator.