If you design or lay out brochures, magazines, newspapers, books, posters, and flyers, you need InDesign. You can create drawings and graphics in Illustrator, but the tools for designing pages with complex, interlocking elements are in InDesign: tight typographic controls, long and multiple text blocks, grid alignment, linking elements across pages, text and object styles, creating and updating links and cross-references, intuitive and powerful text wrap, etc.

Photoshop excels at editing and creating photo-quality images, but lines and text can look fuzzy. It’s not particularly adept at juggling images and text on a page. Illustrator is best for creating drawings that can be resized without loss of quality, but opens only one page at a time.