Sub-inspector (SI), or sub-inspector of police, is a rank used extensively in South Asia: in the police forces of Bangladesh, Pakistan, India, and Sri Lanka, which is primarily based on the British model. It was formerly used in most British colonial police forces and in certain British police forces as well. The rank usually was in charge of a police substation or assisted an inspector.
The rank of sub-inspector was introduced into the Metropolitan Police in the late 19th century. It did not last long, being effectively replaced by station sergeant in 1890. Officers who already held the rank retained it, and were promoted to inspector as soon as a vacancy arose.
In the Metropolitan Police, a rank wearing one star was formerly officially known as a "station inspector" to distinguish it from the more senior rank of sub-divisional inspector that was abolished in 1949.
The Royal Canadian Mounted Police rank of sub-inspector was introduced in 1942 with the insignia of one star, similar to an army second lieutenant. This was changed in 1960 to three stars, similar to an army captain. It was disestablished in the reorganization of 1990, which eliminated the RCMP's subaltern ranks. 
The rank of sub-inspector was eliminated in 1970. 
The rank of sub inspector was replaced after the Rhodesian Unilateral Declaration of Independence with three grades of; patrol officer, senior patrol officer and section officer with one, two, and three gold coloured bars respectively. 
|Sub Inspector of Police|
|Rank group||Lower Subordinate Officers|
|Next higher rank||Inspector of Police|
|Next lower rank||Assistant Sub Inspector|
A sub-inspector (SI) is generally in command of few police personnel (with head constables, the equivalent of corporals, commanding police outposts). It is the lowest rank of officer who, under Indian Police rules and regulations, can file a charge sheet in court, and is usually the first investigating officer. Officers subordinate to them cannot file charge sheets, but can only investigate cases on their behalf. They can be station house officers in some states, like Kerala.
A sub-inspector ranks above an assistant sub-inspector of police (ASI) and below an inspector of police. Most sub-inspectors are directly recruited into the police and have better educational qualifications than lower-ranking police officers.
Specialised units such as the Central Armed Police Forces, State Armed Reserve Police and Armed Battalions use the same rank, but generally these officers do not have any investigative powers. There are also specialist non-investigative officers in other Indian law enforcement agencies, such as sub-inspector (band) and sub-inspector (motor transport).
The rank insignia for a sub-inspector is two (five point) stars, and a red and blue striped ribbon at the outer end of the shoulder straps. This is similar to the insignia of a subedar in the Indian Army. An assistant sub-inspector has one (five point) star, and a red and blue striped ribbon at the outer end of the shoulder straps. This is similar to the insignia of a naib subedar in the Indian Army. The rank insignia for principal sub-inspector and additional sub-inspector are the same.
For the post of Sub-Inspector and assistant sub inspector, a Staff Selection Commission (SSC) recruits eligible candidates on national level in various Central Armed Police Forces like BSF, CRPF, ITBP, CBI, SSB, CISF, and other Central Armed Police Forces. Sub Inspector of Central Armed Police Forces and State police Forces have same scale and pay level. But subedar and Junior Junior Warrant officer of Indian Armed Forces i.e. Indian Army, Indian Navy and Indian Airforce have other pay level and payment privilege which is better than Central Armed Police Forces or State police forces.
In the Royal Malaysia Police (PDRM), the rank of sub-inspector is the senior-most of non-commissioned officers. They are also the lowest ranking police officers to wear their rank insignia on epaulettes on both shoulders. A sub-inspector of the PDRM ranks immediately above a sergeant major (SM) and below a probationary inspector (P/Insp).
In the Nepal Police, the rank of sub inspector is generally the next senior rank from assistant sub inspector (ASI) and is less senior than an inspector. Members holding the rank usually wear an epaulette featuring two silver stars, the same rank badge as a sub inspector in the Armed Police Force.
In the Sri Lanka Police Service, sub-inspector of police (SI) ranks above that of police sergeant major (PSM) and below an inspector (IP). Generally an SI is the officer in charge (OIC) of a small police station, a detachment of police personal or deputy OIC of a larger police station in a metropolitan area.
Most sub-inspectors are directly recruited into the police service as probationary sub-inspectors for one year's training. The basic educational entry requirement is that an applicant has passed the G.C.E Advance Level Examination. Annually, a number of other officers come up through the ranks and are promoted to rank of SI. The rank insignia for a sub-inspector is one star.
In the Romanian Police, subinspector is the lowest commissioned rank, below inspector, and corresponds to the former rank of police second lieutenant (see Romanian Police ranks ).
A non-commissioned officer (NCO) is a military officer who does not hold a commission. Non-commissioned officers usually earn their position of authority by promotion through the enlisted ranks. In contrast, commissioned officers usually enter directly from a military academy, officer training corps (OTC) or reserve officer training corps (ROTC), or officer candidate school (OCS) or officer training school (OTS), after receiving a post-secondary degree.
Sergeant is a rank in use by the armed forces of many countries. It is also a police rank in some police services. The alternative spelling, serjeant, is used in The Rifles and other units that draw their heritage from the British light infantry. Its origin is the Latin serviens, 'one who serves', through the French term sergeant.
Staff sergeant is a rank of non-commissioned officer used in the armed forces of many countries. It is also a police rank in some police services.
Sergeant major is a senior non-commissioned rank or appointment in many militaries around the world.
Police ranks are a system of hierarchical relationships in police organisations. The rank system defines authority and responsibility in a police organisation, and affects the culture within the police force. Usually, uniforms denote the bearer's rank by particular insignia affixed to the uniforms.
Modern Russian military ranks trace their roots to the Table of Ranks established by Peter the Great. Most of the rank names were borrowed from existing German/Prussian, French, English, Dutch, and Polish ranks upon the formation of the Russian regular army in the late 17th century.
Inspector, also police inspector or inspector of police, is a police rank. The rank or position varies in seniority depending on the organization that uses it.
Subedar is a rank of junior commissioned officer in the Indian Army; a senior non-commissioned officer in the Pakistan Army, and formerly a Viceroy's commissioned officer in the British Indian Army.
Assistant superintendent, or assistant superintendent of police (ASP), is a rank that was used by police forces in the British Empire and is still used in many police forces in the Commonwealth. It was usually the lowest rank that could be held by a European officer, most of whom joined the police at this rank. In the 20th century, it was in many territories opened to non-Europeans as well.
Station inspector is a police rank used in some countries.
Superintendent (Supt) is a rank in the British police and in most English-speaking Commonwealth nations. In many Commonwealth countries, the full version is superintendent of police (SP). The rank is also used in most British Overseas Territories and in many former British colonies. In some countries, such as Italy, the rank of superintendent is a low rank.
Fänrik is a company grade officer rank. In the army/airforce, it ranks above sergeant and below lieutenant. In the navy, it ranks above sergeant and below sub-lieutenant. It is equivalent to the specialist officers rank of översergeant. Fänrik means standard-bearer and has been used as a name for the lowest officer rank in the Swedish infantry since the 16th century, with the exception of the years 1835–1914.
The West Bengal Police is one of the two police forces of the Indian state of West Bengal. The other being the Kolkata Police, which has a separate jurisdiction across Kolkata.
The Singapore Armed Forces (SAF) has five rank schemes for active and reservist personnel, with a sixth for the auxiliaries of the SAF Volunteer Corps. The SAF has a unique rank structure as an integrated force, ranks are the same in the Singapore Army, the Republic of Singapore Navy (RSN), the Republic of Singapore Air Force (RSAF), and the Digital and Intelligence Service (DIS).
Gazetted officers include all the Indian Police Service officers which are Class I officers of the cadre and all State Police Services officers of and above the rank of Deputy Superintendent of Police. All are arranged in a hierarchical order.
In the police forces of India, an Assistant of sub-inspector (ASI) is a non-gazetted police officer ranking above a police head constable and below a Sub-inspector. The rank insignia for an ASI is one star, with a red and blue striped ribbon at the outer edge of the shoulder straps. He/she can be an Investigating officer. A.S.I. is often the officer in charge of Police Outposts or "phari" and Investigation Centres. Some police stations carry incharge of GD duty. They make reports of incidents for senior officers.
The rank insignia of the federal armed forces of the Federal Republic of Germany indicate rank and branch of service in the German Army, German Air Force, or the German Navy.
Chief inspector is a rank used in police forces which follow the British model. In countries outside Britain, it is sometimes referred to as chief inspector of police (CIP).
Station sergeant is a police rank senior to sergeant and junior to inspector in some British and Commonwealth police forces. The rank insignia is usually a sergeant's three chevrons surmounted by a crown, or sometimes four chevrons. The Metropolitan Police, which was the first force to introduce the rank, originally used four chevrons, but later changed to a crown over three chevrons, which was identical to the insignia worn by a staff sergeant in the British Army. A police officer holding the rank will be the senior sergeant in a police station, or in some cases the commander of a smaller sub-divisional police establishment.