Some aspects of the history and present role of length-based methods for the study of the growth, mortality and recruitment of fish invertebrate stocks are reviewd. The recently-developed ELEFAN (Electronic Length Frequency Analysis) system of BASIC microcomputer programs is presented and some of its key features are discussed in detail. Examples of the use of teh ELEFAN system are provided; these examples are used to illustrate the need for further research on such length-based systems and to emphasize the need for adequate sampling.