No two skeletons are the same. Firstly, bones and teeth differ in size and shape between individuals. This type of variability, the subject of this chapter and the one that follows, lends itself to recording by measurement, and so is called metric variation. Skeletons also differ in ways which are much more difficult to measure. This type of variability takes the form of minor anomalies of the bones and teeth. These sorts of variants are termed non-metric traits, and are discussed in Chapter 6.