The Document Object Model (DOM) is a browser's programming interface that turns HTML into a tree of objects. Every element on a page becomes a node. When content changes, the browser must update this live structure, a process that can be slow and resource-intensive for complex applications.

React introduced the Virtual DOM to solve this performance bottleneck. It maintains a lightweight, in-memory copy of the real DOM. When a component's state changes, React first updates this virtual representation, avoiding direct and costly manipulations of the actual browser DOM.

React then performs reconciliation, comparing the old and new Virtual DOM trees. It calculates the minimal set of changes needed and applies them to the real DOM in one efficient batch. This approach reduces direct browser interactions, leading to smoother UIs and better developer experience.