Port Arthur is a town and former convict settlement on the Tasman Peninsula, in Tasmania, Australia. It is located approximately 97 kilometres (60 mi) southeast of the state capital, Hobart.

The site forms part of the Australian Convict Sites, a World Heritage property consisting of 11 remnant penal sites originally built within the British Empire during the 18th and 19th centuries on fertile Australian coastal strips. Collectively, these sites, including Port Arthur, are described by UNESCO as "... the best surviving examples of large-scale convict transportation and the colonial expansion of European powers through the presence and labour of convicts."

In 1996, the town was the scene of the Port Arthur massacre, the deadliest instance of mass murder in post-colonial Australian history.

Port Arthur was named after George Arthur, the lieutenant governor of Van Diemen's Land. The settlement started as a timber station in 1830, but it is best known for being a penal colony.

The Port Arthur convict settlement was established in September 1830 as a timber-getting camp, producing sawn logs for government projects. From 1833 until 1877, it was the destination for those deemed the most hardened of transported convicts ― so-called "secondary offenders" ― who had persistently re-offended during their time in Australia. The recalcitrant offenders were sent to Port Arthur, which had some of the strictest security measures in the British penal system but was, nevertheless, also based on the idea that prisoners could be reformed while still being punished.

Port Arthur included a "Separate Prison", which emerged from Jeremy Bentham's theories and his panopticon. The Separate Prison was completed in 1853, and extended in 1855. The layout was fairly symmetrical. It was in a cross shape with exercise yards at each corner. The prisoner wings were each connected to the surveillance core of the prison, as well as the chapel in the centre hall. From the surveillance hub, each wing could be clearly seen, although individual cells could not. In that way, the Separate Prison at Port Arthur differed from the original theory of the panopticon.

The Separate Prison's system also signalled a shift from physical punishment to psychological punishment. The hard corporal punishment, such as whippings, used in other penal stations, was thought to only serve to harden criminals, and did nothing to turn them from their immoral ways. For example, food was used to reward well-behaved prisoners and as punishment for troublemakers. As a reward, a prisoner could receive larger amounts of food or even luxury items such as tea, sugar, and tobacco. As punishment, the prisoners would receive the bare minimum of bread and water. Under this system of punishment, the "Silent System" was implemented in the building. Here, prisoners were hooded and made to stay silent; this was supposed to allow time for the prisoner to reflect upon the actions which had brought him there. Many of the prisoners in the Separate Prison developed mental illness from the lack of light and sound. This was an unintended outcome, although the asylum was built next to the Separate Prison. In many ways, Port Arthur was the model for the penal reform movement, despite the shipping, housing, and use of convicts as slave-labour being as harsh, or worse, than other institutions around the nation.

Port Arthur was also the destination for juvenile convicts, receiving many boys, some as young as nine. The boys were separated from the main convict population and kept on Point Puer, the British Empire's second boys' prison. Like the adults, the boys were used in hard labour such as stone cutting and construction. One of the buildings constructed was one of Australia's first non-denominational churches, built in a Gothic Revival style. Attendance at the weekly Sunday service was compulsory for the prison population. Critics of the new system noted that it seemed to have negligible impact on a prisoner's reformation.