Tagalog Republic (Filipino: Republikang Tagalog; Spanish: República Tagala) is a term used to refer to two revolutionary governments involved in the Philippine Revolution against the Spanish Empire and the Philippine–American War. Both were connected to the Katipunan revolutionary movement.

The term Tagalog commonly refers to both an ethno-linguistic group in the Philippines and their language. Katagalugan often refers to the Tagalog-speaking regions of the island of Luzon in the Philippine archipelago.

However, the Katipunan secret society extended the meaning of these terms to all of the natives in the Philippine islands. The society's primer explains its use of Tagalog in a footnote:

The revolutionary Carlos Ronquillo wrote in his memoirs:

In this respect, Katagalugan may be translated as the "Tagalog nation."

Andrés Bonifacio, a founding member of the Katipunan and later its supreme head (Supremo), promoted the use of Katagalugan for the Philippine nation. The term "Filipino" was then reserved for Spaniards born in the islands. By eschewing "Filipino" and "Filipinas" which had colonial roots, Bonifacio and his cohorts "sought to form a national identity."

In 1896, the Philippine Revolution broke out after the discovery of the Katipunan by the authorities. Prior to the outbreak of hostilities, the Katipunan had become an open revolutionary government. The American historian John R. M. Taylor, custodian of the Philippine Insurgent Records, wrote:

The Katipunan came out from the cover of secret designs, threw off the cloak of any other purpose, and stood openly for the independence of the Philippines. Bonifacio turned his lodges into battalions, his grandmasters into captains, and the supreme council of the Katipunan into the insurgent government of the Philippines.