The laying of a foundation stone is a ceremonial event with a real basis as part of the construction of a structure. It occurs when a specially designated piece of a structure is installed in its place, normally at ground level. This is normally called the "cornerstone" or "foundation stone", although this event may be applied to a similar event involving materials other than stones. Usually some kind of marker or inscription is placed on the cornerstone; this normally shows the date (either of the laying or of projected completion), and often lists key companies or persons involved with the project.

The event is the installation of the designated piece in the structure. An inscription can give a projected completion date, so the date written on the stone need not be the date when it was laid.

A groundbreaking ceremony celebrates the start of the project without requiring installation of a permanent piece. Foundation work begins records the first permanent foundation element, which need not be the ceremonial stone.