Describes the development of Chapter 20 Museums, Libraries, and Archives in the 1999 ASHRAE Applications Handbook (American Society of Heating, Refrigerating and Air-Conditioning Engineers). The handbook is a 'bible' to all Canadian and American mechanical engineers. This chapter is concerned with universally accepted standards for environmental parameters in conservation that has been lacking for many years. Stefan Michalski of CCI (Canadian Conservation Institute) was a participant on the technical committee writing Chapter 20. He was the lead author on sections concerning 'why guidelines are necessary' and the target specifications for temperature and relative humidity (RH) which are elaborated upon in the article. Other issues addressed by the committee include: how to achieve desirable standards; building envelope issues; an abridgement of Ernie Conrad's 'control potential' classification scheme for seven types of building, and they suggested which level of fluctuation control is feasible for each. The chapter provides guidance for both large new museum projects and small historic museums and sheds. It includes recommendations for both temperature and relative humidity. A section on pollution and filtration will be added to the 2002 edition.