AbstractThis paper traces the story of the yard and the metre from pre-Christian times when the basic unit was the cubit up to the present-day use of wavelengths of radiation for defining a standard, and the proposed change to metric units in the United Kingdom.Although much of the story has had to be generalised so as to contain the magnitude of the paper, most of the important comparisons between the basic units are briefly mentioned.Dates, and to some extent lengths, vary somewhat according to the source from which they were gleaned, so that a degree of care needs to be exercised in accepting any of them as being unimpeachable.