Grid systems in web design help provide coherence and usability across different browsers by establishing a regular structure for content, navigation, and layout. There are two main types of grid systems - fluid grids that adapt to any browser window size using relative units, and fixed grids that are resolution-independent using pixel units. Popular grid frameworks like the YUI CSS Grid and 960 Grid System take different approaches to column structure and layout flexibility. Designers must choose a grid based on whether their design needs a fluid or fixed layout, and how much control and versatility they require from the framework.