La Religión del Katipúnan (The Religion of the Katipunan) is a significant work by the Filipino writer, journalist, labor activist, and politician Isabelo de los Reyes (1864–1938). The book was written while De los Reyes was imprisoned in Spain for his suspected involvement in the Philippine Revolution. The work attempts to establish a philosophical and moral foundation for the Katipunan (Kataas-taasan, Kagalang-galangang Katipunan ng̃ mg̃a Anak ng̃ Bayan or Supreme and Venerable Association of the Children of the Nation), the secret society that launched the revolution against Spain. The author presents the Katipunan's principles as a revival of the "ancient beliefs of the Filipinos" (La antigua de los filipinos) and connects the organization's moral and democratic principles (referred to as Bathalismo moderno) to a de-clericalized, nationalistic faith. This second edition, published in Madrid in 1900, includes a previously unreleased second part detailing the organization and "secrets" of the Katipunan and the fundamental principles of Bathalismo and its democratic morality. The publication is a crucial primary source for understanding the religious and political philosophy embraced by some intellectual figures of the revolution and the emergence of a Filipino nationalist identity distinct from Spanish colonial-era Catholicism.
La religión del katipúnan: ó sea la antigua de los Filipinos, tal como ahora la resucita la Asociación de los Hijos del Pueblo (Katipúnas), la promovedora de la Revolución (with the secondary title: Apuntes para un ensayo de Teodícea Filipina)