The Romano-Gothic St Magnus Cathedral, built from red and yellow sandstone, is of international significance.
The foundations were placed in 1137, and the building - dedicated to Magnus Erlendsson, Earl of Orkney - took about 300 years to build.
A team from York-based IIC Technologies has been brought in to carry out the work in Kirkwall.
It will not only produce a detailed image of the building inside and out, but also help in future monitoring of its condition.
And 3D models of the cathedral will also be used as part of a major new exhibition within the Orkney Museum.
Work to produce a detailed three-dimensional survey of a 12th Century cathedral in Orkney is under way.