Louis Jean-Baptiste Lépine (French pronunciation: [lwi ʒɑ̃batist lepin]; 6 August 1846 – 9 November 1933) was a French lawyer, politician and administrator who was Governor General of Algeria from 1897 to 1898 and twice Prefect of Police with the Paris Police Prefecture from 1893 to 1897 and again from 1899 to 1913.

On each occasion he assumed office during a period of instability in the governance of the French State and was seen by his supporters as a man who could bring order. He earned the nickname of "The Little Man with the Big Stick" for his methodology in handling large Parisian crowds. During his periods as Prefect of Police he instigated a series of reforms that modernised the French Police Force. An efficient and clear-sighted administrator, he introduced scientific analysis into policing with reforms in forensic science and the training of detectives.

Lépine was also responsible for convening and re-invigorating the Exposition Universelle whereby an annual competition known as the Concours Lépine was introduced for inventors and innovators to have their work presented and acclaimed; an annual competition that has now had 120-plus editions.

Louis Lépine studied law in his home city of Lyon and in Paris and Heidelberg. He served with distinction in the French Army during the Franco-Prussian War from 1870 to 1871. Serving as a sergeant major at Belfort in the Alsace region, his unit was besieged and continually attacked by the Prussians. It surrendered only after the hostilities had ceased. Lépine was awarded the Médaille militaire for his bravery. He then embarked on a career as a lawyer and public administrator, that included provincial postings as subprefect of Lapalisse, Montbrison, Langres and Fontainebleau and then prefect of Indre, Loire and Seine-et-Oise.

In 1893 Lépine became prefect of police of the Seine (Paris) at a time when Paris and indeed France was politically volatile. His appointment was, in response, to the perceived failure of the previous Prefect Henri-Auguste Lozé to quell serious student riots during the 1893 edition of the Bal des Quat'z'Arts . The riots that had taken place arose out of a trivial incident involving the arrest of an actress Sarah Brown (aka Marie Royer), a student called Nuger and a confrontation with a policeman, the consequence of which was the death of Nuger. On the following Monday, 1,000 demonstrators marched onto the Chamber of Deputies, determined to be provided with an adequate explanation. The Deputies summarily retreated and by the evening a further 1,000 students were outside and by now the mood of the demonstrators had turned hostile. At the end of the day barricades were erected around the district of the Boulevard Saint-Germain.

The police had lost control of the situation and the National Guard was called in to regain control. Several days of bloodshed followed as several important workers’ organisations sided with the so-called students. Within five days of the arrest of Sarah Brown, the students were submerged within a violent mob that was ready to fight for control of Paris. The French Republic seemed in danger and reacted with extreme force with an estimated 20,000 troops deployed to quell the uprising. It was against this backdrop that Louis Lépine succeeded to the Prefecture of Police for Paris with a reputation as a disciplinarian prepared to use the "big stick" to keep Paris under control. Lépine’s tactics were to allow the various factions to march through Paris but to defuse any violent confrontations, by the use of innovative tactics of crowd control that in effect kept the factions, apart and confined to certain areas of Paris, arriving at the planned rendezvous in stages.

Lépine is credited as a founder of modern French policing. At the time of his first tenure the police had become renowned for corruption and low standards: trust between the police and the public was very low. Lépine recognised that if France was not to relapse into military government the relationship between the civil police and the public had to change to become one of mutual trust. The assassination in Lyon in June 1894 of President Carnot, the 5th President of the Republic was the impetus for Lépine to introduce measures to overhaul policing in France. Thus he set an agenda of reform, that was continued during his second period in office, beginning by carefully codified police procedures and regulations, improving the professional quality of the police force with the introduction of examinations and promotions and by introducing forensic science into the work of the detective. It was during his time as prefect of police that fingerprinting became established as a method of identification. The examinations for police that he instituted were very thorough: the tests for example included determining methods of forgery and examining lock components involved in a burglary so as to tell if a lock had been picked. As befits his training as a lawyer, his was the first prefecture to introduce criminology into policing and to examine the psychology of criminals.

Amongst his other innovations, he introduced the white stick for directing traffic and established the river-boat brigade and armed police bicycle units. He installed a series of 500 telephone warning boxes to alert the public and fire services to fire, and he began the reorganisation of traffic movements within Paris by introducing one-way systems and roundabouts.