This chapter shows how Lev Vygotsky introduced and developed the concept of psychological tools. The goal of using psychological tools consists in "the active use of the natural properties of brain tissue". Vygotsky summarizes the specificity of psychological tools with the help of the paired concepts natural and artificial and not, as one might have expected, by the pair natural and cultural. The specificity of psychological tools is examined through an example that Vygotsky developed in Concrete human psychology. The chapter discusses two Vygotskian ideas that are mutually interdependent. The first postulates that all higher mental functions are mediated by psychological tools. The second specifies that all psychology should be concrete in its analysis of psychological tools, both as used to transfer social relations to the psychological realm, and within individuals who use them to impact their own mental processes.