Slavery was the practice wherein sentient beings were treated as property to be bought and sold, enforced by violence or other forms of coercion. It was typical for the owner of a slave to implant him with a device that would kill him if an escape attempt was made. In the more lawful portions of the galaxy where slavery was allowed, if a slave was killed or injured -- in a manner that devalues the slave or prevented him from performing his job -- by a third party, the owner was entitled to compensation from that third party for the depreciated value or the loss of the slave.
Slavery was used by civilizations as disparate as the Infinite Empire of the Rakata, Xim the Despot's empire, the Hutts, the Galactic Empire and the Yuuzhan Vong. To chronicle the use of slavery by various civilizations over the history of the Galaxy is considered by many to be a futile task.
Slavery was made illegal by the Galactic Republic under the Rights of Sentience clause, but continued to exist, particularly in regions not under Republic control, primarily the Outer Rim and Senex Sector. However, that ultimately came crashing down with the birth of Emperor Palpatine's New Order. Under the Empire, non-humans were rounded up and enslaved en-masse. Wookiees, Yuzzem, and Talz were exploited for their strength while the Mon Calamari were used for their famous ship-building skills. Twi'lek girls were also enslaved for their beauty. Many human critics of the New Order were enslaved as well. Ultimately, when the Republic was restored, slavery was once again made illegal.
Slaving was often handled by experienced slaving guilds; three of the most notable were the Thalassian Slavers, the Zygerrian Slavers Guild, and the Karazak Slavers Guild.