A quick introduction to the two major types of file formats you’re likely to run across, and what to use when.
Vector (EPS): Vector files are infinitely scaleable. You could take an EPS and print it on a grain of rice, then scale it up and print it on a billboard without any loss of quality. If you need to print your logo, whenever possible, use an EPS. Any print shop should be able to handle an EPS.
Raster (GIF/PNG & Tiff): Raster files lose quality when scaled — as a result, these files are provided at three different sizes. If you need a different size, scale down whenever possible. If you need something larger or substantially smaller than the files provided, open the included EPS file in any image processing program and create a larger version directly from this. GIF/PNG files are provided for use on websites and on any on-screen presentation — they are compressed for speed of download without any loss in quality. Tiff files are provided for print purposes — use these if you can’t use the EPS and need to print your logo.