The Katipunan (lit. 'Association'), officially known as the Kataastaasan Kagalanggalang Katipunan ng mga Anak ng Bayan (lit. 'Supreme and Venerable Association of the Children of the Nation'; Spanish: Suprema y Venerable Asociación de los Hijos del Pueblo) and abbreviated as the KKK, was a revolutionary organization founded in 1892 by a group of Filipino nationalists Deodato Arellano, Andrés Bonifacio, Valentin Diaz, Ladislao Diwa, José Dizon, and Teodoro Plata. Its primary objective was achieving independence from the Spanish Empire through an armed revolution. It was formed as a secret society before its eventual discovery by Spanish authorities in August 1896. This discovery led to the start of the Philippine Revolution.

Historians generally place the date of its founding in July 1892 shortly after the arrest and deportation of Filipino author and nationalist José Rizal to Dapitan in Mindanao. Rizal was one of the founders of the nascent La Liga Filipina, which aimed for a Filipino representation to the Spanish Parliament. Many members of the Katipunan, including Bonifacio himself, were members of that organization. However, recent discovery of documents of the organization suggest that the Katipunan may have been around by January 1892 but became active by July.

Being originally formed as a secret society, the Katipunan had its members undergo through initiation rites similar to freemasonry. Membership to the organization was initially open only to men; however, women were eventually accepted. The Katipunan had a short-lived publication, Kalayaan (lit. 'Freedom'), which only saw printing in March 1896. During its existence, revolutionary ideals and works flourished, and Filipino literature was expanded by some of its prominent members.

Existing documents suggest that the Katipunan had planned for an armed revolution since its founding, and initially sought support from Filipino intellectuals. In one such incident, Bonifacio planned a rescue for the deported José Rizal in Dapitan in exchange for his support to the revolution, to which Rizal refused. An attempt to secure firearms from a visiting Japanese warship in May 1896 failed to gain anything. In August of that year, Spanish authorities in Manila discovered the organization. Days after, the Katipunan, led by Bonifacio, openly declared war to the Spanish government, starting a three-year long revolution, which marked the beginning of the creation of the nation of the Philippines.

The name "Katipunan" is a short name for "Kataastaasang, Kagalanggalang na Katipunan ng mga Anak ng Bayan" (Supreme and Venerable Society of the Children of the Nation). The Tagalog word "katipunan" (literally, "association", "gathering", "assemblage", or "group") comes from the root word "tipon", a Tagalog word meaning "gathering" or "to gather".

The Katipunan was formed in 1892 by Filipino nationalists Deodato Arrellano, Teodoro Plata, Valentin Diaz, Ladislao Diwa, Andres Bonifacio, and Jose Dizon. It was one of the two groups that was formed after the dissolution of the nascent La Liga Filipina, a nationalist organization formed by Filipino writer Jose Rizal and members of the Propaganda Movement in Spain, following Rizal's arrest and deportation to Dapitan in Mindanao. Most of the Katipunan's early members were also members of La Liga. However, while La Liga advocated for a Filipino representation in the Spanish Parliament, Katipunan's goal was for the archipelago to achieve independence through an armed revolution. Its founders saw that any move for Filipino autonomy from within Spain would be suppressed by colonial Spanish authorities. The other group, Cuerpo de Compromisarios, argued for a peaceful reformation instead. While fundamentally different in their views, the Katipunan decided to name Rizal as their honorary president. Rizal's status was so prominent within the organization that "Rizal" was one of the passwords of the group alongside "Gomburza", a trio of Filipino priests executed in Bagumbayan in 1872 the wake of the Cavite mutiny.

Modern historical consensus generally places Katipunan's formation on the night of July 7, 1892, following Rizal's arrest. It was formed in secrecy on a house in Azcarraga Street (now Recto Avenue) in San Nicolas, Manila. However, it may have been formed on paper as early as January of the same year based on recent documents discovered in the 21st century.

The organization was originally formed as a secret society following freemasonic practices such as its initiation rites and its organizational structure. This may have come from the fact that many of its early members were freemasons themselves. While not directly involved in the organization, prominent Filipino freemason Marcelo H. del Pilar may have influenced the group. Del Pilar is also said to have approved the Katipunan statutes. Filipino historian Epifanio de los Santos, in the 1920s, noted, "It is very correctly stated that Andrés Bonifacio ordered Teodoro Plata to draw up the statutes of the Katipunan, and that he did this with the aid of Ladislao Diwa and Valentín Diaz. After the statutes had been discussed, Bonifacio, with the concurrence of Deodato Arellano, submitted them to Marcelo H. del Pilar for approval. Upon the latter's letter approving the statutes, Bonifacio used the same for the purpose of gaining adepts."