Testosterone is a steroid hormone that is produced in adult males and females, but in males, drastically higher exposure to this hormone during critical periods of development organizes behaviors relevant to reproduction. Levels in adulthood are thought to coordinate the energetic and behavioral investment in mate pursuit and competition for mates, at a cost to other survival priorities. Others suggest that testosterone more broadly affects general status-seeking and dominance within relevant contexts. Yet, the relationship between testosterone and behavior is often misunderstood in both scientific literature and the media, partly due to the conflation of the organizational and more transient effects. With a focus on homo sapiens, I will briefly discuss what is known about testosterone and behavior with respect to 1) long-term exposure during critical windows, 2) sex differences in circulating levels in adulthood, 3) reactivity to social interactions and 4) oral/hormonal contraceptive use in women. Additionally, I will present folk-wisdom and misconceptions about testosterone alongside contrasting empirical evidence, drawing primarily from data collected with over 600 participants in my lab. Finally, I will discuss this knowledge in light of important and timely social-political issues about testosterone as a marker of “biological sex” and sex/gender inclusivity in testosterone research.