Web Components are a set of web platform APIs that allow you to create reusable custom elements with encapsulated functionality. They provide a way to build self-contained components that can be used across modern web browsers, independent of any specific JavaScript framework. The core technologies include Custom Elements, for defining new HTML tags; Shadow DOM, which encapsulates a component's internal structure, styles, and behavior from the rest of the page; and HTML Templates (`<template>` and `<slot>`), which allow for declaring reusable markup. This powerful combination enables developers to create a component-based architecture directly within the browser, promoting modularity and maintainability. Ultimately, Web Components empower developers to extend HTML itself, building truly portable and framework-agnostic UI elements.