This chapter outlines various experimental approaches to manipulating the human brain, which includes damaging selective parts of the brain (\u201cexperiments of nature\u201d such as caused by stroke) or stimulating the brain non-invasively (NIBS, non-invasive brain stimulation). Cognitive neuropsychology is concerned with inferring the structure of cognition from brain lesions (e.g., double dissociations) and in determining structure-function relationships (e.g., what a given region of the brain might be specialized for). The prominent NIBS techniques of transcranial magnetic stimulation (TMS) and transcranial electric stimulation (tES) are introduced from the perspective of a \u201cvirtual lesion.\u201d TMS works by virtue of the principle of electromagnetic induction. TMS causes neurons underneath the stimulation site to be activated. If these neurons are involved in performing a critical cognitive function, then stimulating them artificially will disrupt that function. These methods can be adapted to improve as well as disrupt cognition. <\/p>\n\n\n\n