This is the fourth in a series of manuals designed to facilitate the recognition of the Geometridae of Canada. In the introductory section key characters are given for the identification of Geometridae in adult, larval, and pupal stages. A generalized description of each stage is followed by a key to subfamilies of the Geometridae and a synopsis of the characters of the Ennominae. Keys to the four parts of the Ennominae (sometimes broken down into tribes) as they are to be treated in this series of manuals are supplemented by text descriptions, line drawings, and colour photographs. The distribution of many of the 41 species is shown on 23 maps.A section on the collecting and rearing of Geometridae has been added to the introductory part of this manual to encourage amateurs and young professionals to collect and rear Geometridae. The writer has enjoyed this part of the work more than any other and would like to see others share in the fun.