Readmore.js : jQuery plugin for Collapsing and Expanding Text Blocks

A smooth, lightweight jQuery plugin for collapsing and expanding long blocks of text with “Read more” and “Close” links.

The required markup for Readmore.js is also extremely lightweight and very simple. No need for complicated sets of divs or hardcoded class names, just call .readmore() on the element containing your block of text and Readmore.js takes care of the rest.