The various species of Crustacea display great differences in maximum size, and the means by which this is delimited have been investigated. Two distinct strategies of growth exist. Some species have indeterminate growth and continue moulting indefinitely. In these the percentage moult increment declines and the intermoult period increases with size, thereby limiting growth: the respective rates of decline and increase determine the final size. Others have determinate growth and eventually cease moulting, usually at the time of maturity: this termination of moulting stops growth, and in such species the percentage moult increment does not decline appreciably with size. The advantages and disadvantages of the two strategies of growth are discussed.