 The meaning of the terms given at the start of the introduction may at first seem clear, but conceptual questions have accompanied or been implied by the use of the terms since their introduction to English-language readers by Johannsen’s (1911) “The Genotype Conception of Heredity” and up until the present. How does an individual organism’s DNA influence the processes of development of its traits over its lifetime—processes that also involve other influences? How can an individual organism’s traits be used to identify its DNA sequence? Why are the terms genotype and phenotype still used if they simply refer to the individual’s DNA and traits? One answer to this last question is that what counts is less the meaning of the terms than what their use has come to signify, in particular, that certain issues have been resolved: the barrier between the organism’s life course and DNA transmitted to the next generation; evolution is change in frequencies of genes or DNA sequences in populations over time; development of traits will eventually be understood in terms of a composite of the effects of DNA on the organism; what counts is what is underneath or inside the observable surface; and findings about heredity derived using one meaning of terms affirm findings derived using a different meaning. How firmly resolved are these issues? If one wants to open them up for further scrutiny, it could be helpful to question the meaning of genotype, phenotype, and the distinction between them.