The works of the four Van der Laan architects are described in this book in context. Leo van der Laan, together with his son Jan, designed hundreds of buildings, mainly in Leiden and its surroundings. They were known as Catholic traditionalist architects, who built mainly within their own Catholic column. Their work shows a clear development, with their approach always showing something very unique within the prevailing style of their contemporaries. Dom Hans van der Laan, together with his brother Nico, developed a fully developed theory of the relationship between architecture and liturgy. By considering their system of proportions of plastic number not in isolation, but within the context of the larger picture of the God-created world, they helped generations of Catholic architects reflect on the essence of architecture. Their designs continue to attract attention for their simplicity and particular style.