Abstract: The present invention comprises a stair construction and method in which the stair includes at least one stringer assembled in situ from a plurality of stringer units, treads supported on the stringer, and a hand rail comprised of a plurality of hand rail units or sections secured together in situ. The use of modular construction, with the parts assembled in situ on a job site, enables the components to be manufactured in a factory and then shipped in convenient packages to the job site for assembly. This enables relatively complex stair designs, such as spiral and circular stairs, as well as more conventional straight stairs to be employed in construction without concern for bulky and difficult to handle packaging and shipping, or the need for skilled carpenters using special tools to construct such stairs on the job site.