The Document Type Declaration, or DOCTYPE, is an instruction in an HTML document that specifies the version of HTML or XHTML being used. It helps browsers to correctly render and display the document by indicating the rules and specifications to follow. The DOCTYPE declaration is placed at the very beginning of an HTML document, typically within the `<!DOCTYPE>` tag.
Here is an example of a DOCTYPE declaration for HTML5:
<!DOCTYPE html>
<html lang=”en”>
  <meta charset=”UTF-8″>
  <meta name=”viewport” content=”width=device-width, initial-scale=1.0″>
  <title>HTML DOCTYPE Example</title>
  <!– The content of the HTML document goes here –>

HTML Document Type Declaration - Example of a DOCTYPE declaration for HTML
In this example:

– `<!DOCTYPE html>` specifies that the document follows the HTML5 standard.
– The HTML document is then contained within the `<html>` tags.
– The `lang=”en”` attribute in the `<html>` tag indicates that the document is written in English.
The DOCTYPE declaration is not an HTML tag; it’s an instruction to the browser about the version of HTML or XHTML in use. Different versions of HTML have different DOCTYPE declarations. For example, the DOCTYPE for HTML 4.01 might look like:
It’s important to use the correct DOCTYPE declaration for the version of HTML or XHTML you are using, as it helps browsers interpret and render the content according to the specified standard. For modern web development, HTML5 is the standard, and the `<!DOCTYPE html>` declaration is commonly used.