A brief description of the jackknife technique is given, together with a resume of its underlying theory, reputed advantages and disadvantages and its general properties. Several examples are then given to illustrate the application of jackknifing to data arising from real problems, including estimating parameters of mathematical models, dealing with ratios of components of variance and the evaluation of sampling errors from a multi-stage survey. The value of the jackknife is assessed in the light of the results obtained, and by comparison with corresponding results from "orthodox" methods of analysis.