ai – Adobe Illustrator: Vector based, editable, native file (Mac: Illustrator, Freehand etc. PC: Illustrator, Corel Draw, etc.). Your vendors (printers, web designers, silk screen printers, etc.) will use this file.

eps – Vector based, importable file for most desktop publishing software (will work with Mac and PC). These files can be “placed” or “imported” into most desktop publishing software (Microsoft Word, QuarkXpress, InDesign, etc.). Your vendors (printers, web designers, silk screen printers, etc.) will use this file.

pdf – Portable Document Format
This is a multiplatform file (viewable by both Mac and PC through adobe acrobat reader). This format is used when one party may not have the same software on their computer as used to create the original file. Your designer may use this file type to send you proofs and your vendors (printers, web designers, silk screen printers, etc.) may use this file.

jpg – 72 dpi web-ready file (will work with Mac and PC). These files are for Web use only. These files are the correct resolution for use on your website and for email.

gif – 72 dpi web-ready file (will work with Mac and PC). These files are for Web use only. These files are the
correct resolution for use on your website and for email.

tif and/or bmp – 300 dpi, raster-based file (will work with Mac and PC). This file can be opened by some Mac and PC illustration and image software (Illustrator, FreeHand, PhotoShop, ImageReady, etc.), and can be “placed” or “imported” into most desktop-publishing software.

png – for Portable Network Graphics.
It’s a lossless bitmap image format that is popular on the World Wide Web and elsewhere. PNG was largely developed to deal with some of the shortcomings of the GIF format and allows storage of images with greater color depth and other important information.