Chaining methods is a core feature of D3.js that lets you apply several operations to a selection in a single, streamlined statement. When you chain methods, each method call returns the selection, allowing you to immediately call another method on the same set of elements. This approach makes your code much more concise and readable, reducing repetition and making it easier to understand the sequence of transformations or styling you are applying. Instead of writing multiple separate statements to set attributes and styles, you can chain them together, clearly showing the flow of changes applied to your elements.