Modern church architecture is characterized by simplicity, as well starkness, and in many cases uses steel, glass and reinforced concrete as building materials.
In 1963, decrees of the Second Vatican Council encouraged active participation by the faithful in the celebration of the liturgy which some architects interpreted as the need for a drastic movement away from longitudinal floor plans used in most classical church architecture styles. As a result, many, but not all, churches built in the Modern style have centripetal floor plan and more open configuration where the altar and focal celebration are more accessible to the attendees. The style allows for wide degrees of variation and interpretation; and can achieve stunning effects with modern construction techniques such as soaring concrete steeples and voluminous lighting from nearly all-glass side walls.
Example illustrated: Cathedral of St. Mary of the Assumption in San Francisco, California
See image with the smooth, white walls of formed concrete, minimal windows and unique design of a the formed-concrete steeple in the shape of a cross.
Another example: Cathedral of Brasilia in Brasilia, Brazil