The biologist H. Maturana developed a theory of knowing, the Biology of Knowing, funded on the question “how we do what we do”? This allow us to explain the cognitive effectivity of living and human beings as the conditions that preserve the history of mutual congruent structural changes as long as autopoietic unity and its containing environments do not disintegrate. From the phenomenon of constitution of living we developed an explanation about the arising of human phenomenon. This allowed us to formulate a theory of designing, the Biology of Designing, which demonstrates how to design and build artifacts and environments which promote the cognitive effectivity of their users as a byproduct of the own phenomenon of humannessing that constitutes them as particular human beings. Finally, this theory is applied to the construction of a new methodology of designing and engineering of conversation artifacts and environments (computer artifacts and environments).