Psychoanalytic theory is one of the world’s grand theories. Not merely clinical, psychoanalytic general theory introduces two momentous contributions. One, the key role of primary processes, is the subject of this issue and this article. Here I maintain that primary processes are a-rational, not irrational, hence not pathological, but developmental, and prevalent also in nonhuman animals. I review empirical evidence supporting the existence of such primary process mentation. Brief accounts are then given of several interdisciplinary bridges to mind and behavior studies based on this expanded view of a-rational primary processes. Interdisciplinary areas discussed range from the biological (conditioning and evolutionary considerations) to vexing issues in the philosophy of mind and the philosophy of action (agency and belief).