* The Society of the Divine Word (SVD): This is the largest Catholic missionary society in the world, founded in 1875. Janssen's main focus was on missionary work, and he wrote numerous articles and books on this topic, including:
* "The Divine Word: A History of the Society of the Divine Word"
* "The Missionary Ideal"
* "The Mission of the Church"
* The Missionary Sisters Servants of the Holy Spirit (SSpS): He also founded this congregation in 1889, with a focus on education and healthcare.
While Janssen is known for his organizational work and leadership, he is not considered a prolific writer. He wrote primarily for the benefit of the congregations he founded, rather than for a wider audience.
Therefore, while a comprehensive list of his writings might be challenging to find, the titles mentioned above give you a good idea of the type of topics he addressed in his works.