||In studying the dynamics of populations, whether of animals, plants, or cells, it is crucial to allow for intrinsic delays, due to such things as gestation, maturation, or transport. MacDonald takes this opportumity to address one of the fundamental questions in the analysis of the effect of delays, determining whether they affect the stability of steady states. The analysis is presented for one or two such delays treated both as discrete, where an event that occurred at a precise time in the past has an effect now, and distributed, where the delay is averaged over the population's history. Both of these types occur in biological contexts. The method used to tackle these questions in linear stability analysis that leads to an understanding of the local stability. By avoiding global questions , the author has kept the mathematical prerequisites to a minimum of advanced calculus and ordinary differential equations.