There are 6 types of CSS selectors: simple, class, generic, ID, universal, and pseudo-class selectors. Simple selectors apply styles to single elements. Class selectors allow assigning different styles to the same element on different occurrences. ID selectors define special styles for specific elements. Generic selectors define styles that can be applied to any tag. Universal selectors apply styles to all elements on a page. Pseudo-class selectors give special effects like focus and hover.