Though often described as a secret police, the Tal Shiar operated openly and often publicly. Their methods used to control the populace and subvert rebellion and ensure loyalty were based on fear. Allowed to run with no oversight from the Romulan military branches nor the centralized government, the Tal Shiar's tactics and methods are considered brutal by Terran standards.
Their name stems from the ancient Vulcan method of execution, Tal Shaya, neckbreaking. Though Rihanha is very similar to Ancient Vulcan, a more modern translation would be similar to "talla shiar" or duty to the empire.
The current state of the Tal Shiar is not fully known. Since the events of the Dominion War followed by the Hobus Supernova, the Tal Shiar has sustained heavy loses and it is believed their influence has shrunk. In contrast, some theories posit that what is left of the Romulan Empire is completely run by the Tal Shiar.
A complete picture of the Tal Shiar's structure is not, and may never, be fully understood. It is known that they have a Chairman who often, though not as a rule or standard practice, serves on the Continuing Committee. The exact nature of the Chairman's duties is unknown. Below this, next to nothing is known about their structure. It is known that individuals hold rank similar to their Navy counterparts. If this rank is official inside or outside the organization is what is unknown. It is also known that their command influence supersedes actual ranked officers in the field. The source of this command authority is unknown but believe to date back far in its history. No known written charter in the Romulan government officially endorses the practice though it is treated as common law. This over arching command authority has caused mistrust of the Tal Shiar both within the Romulan Star Navy and the Romulan Senate. Despite this mistrust, many follow orders for fear of exile, torture, or death at the hands of the Tal Shiar. It is known that the Tal Shiar does have a fleet of their own ships consisting mostly of D'Deridex Class warbirds.
A full history of the Tal Shiar would be impossible to collate. By their very nature, keeping written record and history would be considered disadvantageous. What history is known has only come to knowledge within the last century (as of 2398).
During the 2360's, it is known that the Tal Shiar were instrumental in quieting building dissent on Romulus for the reunification of the Romulan and Vulcan people. Unification leaders were actively and publicly sought out. Many kidnapped in broad day light and never to be seen again. During this time, an exploit was found in that spies were able to infiltrate a surgically modified person posing as a Tal Shiar agent. Because of the Tal Shiar's command authority, this spy was able to single-handedly take command of the warbird Khazara and deliver into the hands of the Federation, the defector Vice-Proconsul M'ret.
The 2370's saw the largest and most visible operation in known Tal Shiar history. After having made a deal with Starfleet regarding use of a cloaking device on the Starfleet Vessel Defiant in exchange for all intelligence from the Gamma Quadrant in what appeared to be a gesture for future collaboration and peace, the Tal Shiar had secretly aligned with the Cardassian Obsidian Order, a group of similar nature to the Tal Shiar. In addition to providing a fleet of ships to the joint effort to attack the homeworld of the Founders, the Tal Shiar assisted the Obsidian Order by openly assassinating members, and former members, of the Obsidian Order who opposed their current goals. Ultimately this union was unsuccessful as both organizations had been infiltrated by changeling spies, leading to the disastrous ambush in the Omarion Nebula.
Since the Hobus Supernova, only rumors of Tal Shiar operations have existed. As is the nature of Romulans in general, anyone who is operating in a "secret" manner is often accused of being Tal Shiar, most often of late as a joke. Their current numbers, strength, and capabilities is unknown.