ZIP is a popular file format that is supported by many software programs on both Mac and Windows. We ZIP files for two reasons: to make them smaller, and to combine multiple files into a single file. Have you ever noticed, however, that sometimes zipping a file actually makes it bigger? The reason is that file formats such as JPG (for images) and MP3 (for audio) are already compressed. And the exact way the ZIP does its compression often results in a larger file. But in these cases, zipping still does the job for combining multiple files into one. For a more detailed explanation of why and how, read Ask Leo’s article Can I Zip My Pictures or MP3 Files to Save Space?.