Pigeons were trained to discriminate between the presence and absence of a pigeon in photographic displays projected on a response key. Irrelevant cues were reduced as much as possible, while the differences between the objects were of sufficient variety and complexity to ensure that mastery of the discrimination would require the use of a concept. The Ss learned this discrimination very rapidly. On a test given following training, the Ss showed almost complete transfer to new displays containing fancy breeds of pigeons and showed significantly less transfer to new displays containing other species of birds. These results indicate that discrimination was based on a concept of “pigeon.”