An attempt is made, within a limited space, to indicate the importance of taxonomy, especially of the Spermatophyta, to the more recently developed branches of biology, and to show that these in turn are reacting on taxonomy. Certain basic logical problems are discussed and a via media between extreme lines of development is suggested. The interactions between taxonomy and cytology, genetics, ecology, palaeontology, phylogeny, biometrics, and physiology are discussed briefly with a few selected examples. Practical suggestions for improving taxonomic methods and for increasing co-operation between different branches of biology are made in various places throughout the text. Lastly, proposals are made that in practice should lead gradually and some way towards an “omega” or perfected taxonomy, which, idealistically, should be a completed classification of all biological knowledge.