The article discusses Karl Popper’s account of Lamarckism. In this article I use Popper’s published and unpublished statements regarding Lamarckism as well as his correspondence with the Australian immunologist Edward Steele and other biologists to examine why Popper was interested in Lamarckism, how his account of Lamarckism can be understood in the context of his philosophy, and what, if any, new context Popper provided for the discussion of this abandoned doctrine. I begin by discussing Popper’s frame of reference regarding Lamarckism, (...) examining how it changed following his involvement with different “transitory groups” of biologists concerned with redefining the boundaries between traditional disciplines. I then discuss Popper’s account of Lamarckism in positioning it in relation to three aspects of his philosophy: his distinction between the principles of induction/instruction and deduction/selection, his distinction between scientific and teleological concepts, and his concept of progress in science. Then, I follow the debate concerning Steele’s Lamarckian experiments with a closer look at Popper’s role and his position in this controversy. I conclude that Popper’s writings provided a new context for the discussion of Lamarckism in the 1970s and 1980s, thus making it “scientifically acceptable” again. I preface this discussion by a brief outline of Steele’s Lamarckian hypothesis and Popper’s comments on Steele’s work. (shrink)