What are the advantages/disadvantages of Sass/Compass over LessCSS?

To start with, Sass (http://sass-lang.com/) is not brand new. It has been in development for around 4 years and is a well maintained, mature and thought-out solution to many lacking areas of CSS and the newer CSS3 syntax. With Sass you can easily convert CSS to Sass using sass-convert and even then you can convert Sass to and from either of its 2 syntaxes .scss or .sass. Not only that, ultimately the end point of Sass compiles to CSS with options for 4 output styles (http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html#output_style): nested, expanded, compact and compressed. The magic happens when you add nested rules, variables, mixins, selector inheritance and to top it all off ... Compass. Compass (http://compass-style.org/), is a CSS authoring framework that sits on top of the Sass language that allows you to quite literally, create any type of "framework" for doing things with CSS. Some examples include: Fancy Buttons (https://github.com/imathis/fancy-buttons) - A framework for creating Fancy looking buttons quite easily Grid Coordinates (https://github.com/adamstac/grid-coordinates) - A highly configurable Sass based CSS Grid Framework Generator Susy (https://github.com/ericam/compass-susy-plugin) - A semantic CSS grid system for designers built entirely native to Compass http://960.gs (https://github.com/chriseppstein/compass-960-plugin) - A well known 960px based grid system by . Blueprint CSS - A well known, full-feature CSS framework As far as I know, Less (http://lesscss.org/) hasn't even thought about things like frame-working and such - but I have to be honest here. I'm not one to ask about the finite details of Less simply because I have never tried it due to common warning signs when adopting new technologies such as: Project maturity User base Flexibility Usefulness, etc. For me, Sass and Compass clicked right away and I never looked back. Nathan Weizenbaum (http://nex-3.com/) and have been phenomenally dedicated to the development, maintainence and usefulness of Sass and Compass. To add to that, a vibrant community of folks have proped up around them to support their efforts and develop the ecosystem. To me, Sass and Compass are the future. When you have your "ah ha" moment, get in touch with me and let me know.

The existing answers do a great job of comparing the syntax and the relative maturity of the two platforms. So I'm not going to go there. Another thing to consider is the platform that you're working with.  It seems that there are Rails and PHP implementations for both, but only SCSS compilers exist for Django/Python. If you're using Node.js or want to compile your stylesheets in javascript, LESS is more mature and probably the better choice. Compare javascript SCSS: https://gist.github.com/820035 and LESS: http://lesscss.org/ I personally found the syntax/capabilities to be about the same; I ultimately went with LESS because I liked the syntax and it matched my platform. Either way, your CSS will be awesomed.

Just wanted to chime in and say that initially I was skeptical about CSS preprocessors. I thought maybe I might be able to warm up to Scss, but after having used Sass, I like it quite a bit. Given the choice, I would use Sass (not Scss) over Less. It is more terse. And, if you're going to switch to a preprocessor instead of writing vanilla CSS, you might as well choose on that greatly reduces keystrokes.

You can find an updated version of 's comparison at  https://gist.github.com/820035 by Wil Moore. I like more less.js syntax but it looks like SASS is better at the current time.

For me the most important difference is that LESS offers limited conditionals and control structures, which are required for building up complex mixins. It is sometimes said that LESS is a good pre-processor to get started with (if you haven't used a pre-processor before) and I've found that to be true. Once you start to hit the limits of LESS you move on to SASS or to the alternative project Stylus.