When to use Flexbox and when to use CSS Grid

CSS Flexbox excels at one-dimensional layouts for aligning items in rows or columns, making it perfect for UI components and simple alignment tasks. CSS Grid handles two-dimensional layouts with both rows and columns simultaneously, ideal for complex page structures. The key principle is using Grid for overall layout architecture and Flexbox for component-level alignment. Both systems can be combined effectively - Grid for the main page structure and Flexbox within individual sections for precise element positioning. Modern web development benefits from understanding when each tool serves its purpose best rather than trying to force one solution for all layout needs.