This Fact Sheet presents a brief overview of provincial readjustments of the Alberta Survey Control network as well as national (cross-Canada) readjustments that define the reference frame in Canada (and Alberta). It is important to note that with the advancement of least squares adjustment software in the 70’s and 80’s, the ability to carry out large scale readjustments has increased dramatically. This increase is reflected in the implementation and refinement of various 2-dimensional (NAD27) and 3-dimensional (NAD83) reference frames in Canada (including Alberta).