Last updated July 28, 2011. Created by Shai on July 24, 2005.
Edited by LeeHunter, tim.plunkett, silverwing, webchick. Log in to edit this page.
This page explains Drupal's version numbering scheme for both Drupal core and contributed modules. It is designed to help you understand what the various version numbers mean and how you can use this information when building a Drupal site.
Which version of Drupal core should I install?
In brief, you should always run one of the recommended official releases. These can be found at the Drupal Project page.
At any given time, there are two major release series of Drupal which are supported. Currently, these are Drupal 6 and Drupal 7. Updated versions of each of these are issued on a regular basis. For example, within the Drupal 6 series, several versions have been and will continue to be released: 6.0, 6.1, 6.2, etc. These versions are sometimes collectively referred to as "6.x"; however, they are not all equal. The newest version in each series fixes problems that were discovered since the previous version, and these fixes sometimes include critical security updates. Thus, regardless of whether you are using Drupal 6 or 7, you should always run the most current version in the series.
In deciding between Drupal 6 and Drupal 7, several factors should be taken into consideration. Drupal 7 is newer, will be supported longer, and contains more features and enhancements than Drupal 6; therefore, if all else is equal, use Drupal 7. However, the releases of contributed modules, themes, translations, and installation profiles compatible with each major Drupal release series sometimes lag behind Drupal itself, so if the functionality you need is not yet available for Drupal 7, this may affect your decision.
Drupal 8 is currently in the early stages of development and is not yet fit for production use. If previous patterns continue, a stable version (Drupal 8.0) will likely be released sometime in 2012. Once that happens, Drupal 6 will no longer be supported or receive security updates, and you will need to upgrade your Drupal 6 sites to Drupal 7 at that time.
Which version of contributed modules, themes, and translations should I install?
You usually should run one of the "official releases" from the module, theme, or translation's project page, because these are the versions that are currently supported by the maintainer. Note that when examining a particular release available on these pages, the first part of the version number shows you which major release series of Drupal core a module, theme, or translation is compatible with. For example, a module with a version number of 6.x-1.2 will only work with Drupal 6, whereas a module with a version number of 7.x-1.2 will only work with Drupal 7.
When is the next release?
New stable releases of Drupal core are scheduled for the last Wednesday of each month. A new release will only come out on this date if it's deemed by the Drupal core maintainers to contain enough important bug fixes to warrant a release; if not, you're safe until the next month! :)
If a release is warranted, a "code freeze" will be called a few days prior to the release date, and the impending release will be announced via the @drupal Twitter account and Planet Drupal. This makes a great time to update to the latest code in the branch for your version of Drupal, and help make sure the code is solid!
Exceptions to this schedule may be made in case of security vulnerabilities being actively exploited in the wild, or severely critical bugs that prevent Drupal from being used.
How do I know which version of Drupal I'm running?
If it's available, go to Administer (or Administration) >> Reports >> Status report. This will list your version number if you have Drupal 6.0 or later. In Drupal 5.x and earlier, the path to go to is Administer >> Logs >> Status report.
Failing that, look for a file called CHANGELOG.txt in the root of your Drupal directory and open it up to find the version you are running.
If CHANGELOG.txt is missing, you can also check in system.module for a line at the top like:
define('VERSION', '5.5');
If this is present, it will tell you which version you are running. If not, you have a version earlier than 4.7.2.
How do I know which version of a module or theme I'm running?
You can see the versions of your installed modules and themes on the modules and themes administration screens. In Drupal 7, go to Administration >> Modules or Administration >> Appearance, and you will see a column listing the version number. (In Drupal 6, the equivalent pages can be found at Administer >> Site building >> Modules and Administer >> Site building >> Themes.)
What about upgrading and backwards compatibility?
For more details read this overview of Drupal's philosophy on backwards compatibility.
More details
The pages below have some more details for advanced users.