In 1905, Pius X in his letter Acerbo nimis mandated the existence of the Confraternity of Christian Doctrine (catechism class) in every parish in the world.

The Catechism of Pius X is his realisation of a simple, plain, brief, popular catechism for uniform use throughout the whole world; it was used in the ecclesiastical province of Rome and for some years in other parts of Italy; it was not, however, prescribed for use throughout the universal church.
The characteristics of Pius X were "simplicity of exposition and depth of content.
Also because of this, Pius X's catechism might have friends in the future."
The catechism was extolled as a method of religious teaching in his encyclical Acerbo nimis of April 1905.

The Catechism of Saint Pius X was issued in 1908 in Italian, as Catechismo della dottrina Cristiana, Pubblicato per Ordine del Sommo Pontifice San Pio X. An English translation runs to more than 115 pages.

Asked in 2003 whether the almost 100-year-old Catechism of Saint Pius X was still valid, Cardinal Joseph Ratzinger said: "The faith as such is always the same.
Hence the Catechism of Saint Pius X always preserves its value.
Whereas ways of transmitting the contents of the faith can change instead.
And hence one may wonder whether the Catechism of Saint Pius X can in that sense still be considered valid today."
In 1905, Pius X in his letter Acerbo nimis mandated the existence of the Confraternity of Christian Doctrine (catechism class) in every parish in the world.
The Catechism of Pius X is his realisation of a simple, plain, brief, popular catechism for uniform use throughout the whole world; it was used in the ecclesiastical province of Rome and for some years in other parts of Italy; it was not, however, prescribed for use throughout the universal church. The characteristics of Pius X were "simplicity of exposition and depth of content. Also because of this, Pius X's catechism might have friends in the future." The catechism was extolled as a method of religious teaching in his encyclical Acerbo nimis of April 1905.
The Catechism of Saint Pius X was issued in 1908 in Italian, as Catechismo della dottrina Cristiana, Pubblicato per Ordine del Sommo Pontifice San Pio X. An English translation runs to more than 115 pages.
Asked in 2003 whether the almost 100-year-old Catechism of Saint Pius X was still valid, Cardinal Joseph Ratzinger said: "The faith as such is always the same. Hence the Catechism of Saint Pius X always preserves its value. Whereas ways of transmitting the contents of the faith can change instead. And hence one may wonder whether the Catechism of Saint Pius X can in that sense still be considered valid today."
Pope Pius X