When you want to work with more than one element at a time in D3.js, use the d3.selectAll function. This method allows you to select every element that matches a given CSS selector, whether it is by tag name, class, or id. Unlike d3.select, which only selects the first matching element, d3.selectAll creates a D3 selection that contains all matching elements. This is especially useful when you need to apply the same style, attribute, or behavior to a group of elements, such as highlighting all list items or updating every bar in a chart. You can use standard CSS selectors inside d3.selectAll, giving you flexibility to target exactly the elements you need. The result is a D3 selection, not a plain JavaScript array, so you can continue to chain D3 methods and perform operations efficiently on all selected elements.