Transmission is a free lightweight BitTorrent client which features a simple interface on top of a cross-platform back-end. It is free and open source software, mostly licensed under the MIT License. Transmission runs on Linux and other Unix-like systems (GTK+ interface), Mac OS X (Cocoa interface) and BeOS/ZETA (native interface). On 14 January 2008, it was adopted as the default Bittorrent client in the popular Linux distribution Ubuntu. An unofficial port of Transmission (with a command-line interface) to the iPhone OS was accomplished on March 3, 2008. As of January 10, 2008, Transmission has had over 230,000 downloads. It is the most popular BitTorrent client downloaded from Mac software website MacUpdate.
Transmission uses a smaller amount of system resources than many other BitTorrent clients (such as Vuze). The project aims to strike a balance between providing useful functionality without feature bloat. Keeping the interface simple and intuitive on all platforms is a key design goal.
Transmission, in the most general sense, allows users to download files from the Internet and upload their own files or torrents. By grabbing items and adding them to the interface, users can create queues of files to be downloaded and uploaded. Within the file selection menus, users can customise their downloads down of components of individual files. Transmission also has functionalities for seeding, which refers to the process of re-uploading downloaded content.
- Selective downloading and file prioritizing
- Encrypted peer connections
- Torrent file creation
- Peer exchange (compatible with Vuze and μTorrent)
- Automatic port mapping (using UPnP/NAT-PMP)
- Fast Resume - with peer caching
- Dynamically bans bad peers, and can use an IP blocklist
- Single listening port for all torrents
- Global/individual bandwidth caps
- Sorting/filtering options
-  tracker support
Mac OS X specific
- Transfer Management
- Downloading and seeding queues
- Basic scheduling
- Auto-seeding options
- Dock and Growl notifications
- Quick Look technology built-in.
- Customizable toolbar
- Advanced progress box
- Automatic updates using Sparkle
- Universal Binary
Daily Mac OS X build and source tarballs are available online The project has a forum where users can discuss support issues and make features requests. They also have an IRC channel, #transmission, located on Freenode.
The Transmission back-end (libTransmission) also serves as the basis of the shareware
Mac client Xtorrent, and the Transmission daemon
. The daemon supports a web front-end
called Clutch. Older versions have been ported to form the basis of the update system for the video game Metal Gear Solid
,, as well as the backend for ImageShack
's BitTorrent service
libTransmission also utilizes some third party libraries, including libevent
Version 0.6.1 of Transmission did not strictly adhere to the complete BitTorrent specification. This resulted in the banning of that version from many private trackers. The issues were resolved in the subsequent 0.70 release.