Abstract. D. Tyteca & J.-L. Gathoye.- The Dactylorhiza of Western Europe: A biostatistical approach [Natural. belges (Orchid. 2) 69 (1988): 65-97]. In a introductory part, a few basic concepts and techniques of numerical taxonomy are briefly recalled in simple, non-mathematical terms. The main part of the paper is devoted to the application of statistical methods to fifteen taxa of Dactylorhiza in Western Europe, in order to illustrate how the study of the relationships between closely allied taxa, as well as the identification of critical populations at adequate taxonomic levels, can benefit from such methods. By means of cluster analysis, the more or less 60 populations studied lend themselves to very “natural” groupings, with regard to the present state taxonomy. A few critical aspects are dealdt with greater detail: (1) relationships between D. incarnata, its var. hyphaematodes, and D. cruenta; (2) within the D. majalis group: variability of D. sphagnicola and D. praetermissa; (3) within the D. maculata group: discussion of D. maculata subsp. elodes; variability of D. fuchsii; chorological and systematical boundaries of D. saccifera with respect to D. fuchsii in Italy. A few concluding remarks are drawn about the contributions and limitations of biostatistical methods, as examplified by the taxa and populations studied.