v1.5.1 is a new release with improved speed and several bugfixes

Details of changes, and upgrade instructions, explained here: http://www.zen-cart.com/showthread.php?200259-Zen-Cart-v1-5-1-Released

v1.5.0 is a new release with tightened security and feature enhancements.

Details available here: http://www.zen-cart.com/forum/showthread.php?t=190424

Upgrading should follow normal upgrade procedures as posted at http://www.zen-cart.com/upgrades

Please visit the Zen Cart support forum for release details. http://www.zen-cart.com/forum/showthread.php?p=952207#post952207

See release notes and announcement on the Zen Cart Forum http://www.zen-cart.com/forum/showthread.php?p=940745#post940745

For details visit the Zen Cart Support Forum: http://www.zen-cart.com/forum/showthread.php?p=922779#post922779

v1.3.9e contains several bugfixes. Details: http://www.zen-cart.com/forum/showthread.php?p=914125#post914125

Upgrading is as easy as replacing the files that have changed since v1.3.9d.

v1.3.9d includes several bugfixes over v1.3.9c

Details available here: http://www.zen-cart.com/forum/showthread.php?t=156619

Upgrading is a simple matter of replacing the changed files since the previous version.

v1.3.9c includes several bugfixes over v1.3.9b

Details available here: http://www.zen-cart.com/forum/showthread.php?t=155307

v1.3.9b includes several bugfixes over v1.3.9a, including repairs to Maestro support with 3D-Secure

Details available here: http://www.zen-cart.com/forum/showthread.php?t=154039

v1.3.9a includes speed improvements, security fixes, PHP 5.3 compatibility, and much more.

Details on what's new in this release can be read here:
http://www.zen-cart.com/forum/showthread.php?t=153088

Download Zen Cart v1.3.9 here: http://sourceforge.net/project/showfiles.php?group_id=83781&package_id=171544