A SAFE is a contract that converts into stock at a future priced round—not stock, not debt—and its famous simplicity hides mechanics that routinely reallocate ownership in ways founders and investors do not expect. This overview defines the instrument, walks the four negotiable levers (valuation cap, discount, most-favored-nation right, and conversion trigger), and works the conversion math for caps and discounts with fresh, labeled hypotheticals. It explains the 2018 shift from pre-money to post-money SAFEs and why that quiet change moved dilution risk onto founders, then dissects two traps the standard forms leave unsolved: the phantom liquidation preference and the multi-tranche "SAFE pileup." It compares SAFEs to convertible notes feature by feature, and lays out the securities-law reality that a SAFE is a security sold under Section 4(a)(2) and Regulation D, subject to Form D, blue-sky notice, and the anti-fraud rules. It closes with the unsettled tax picture, an honest accounting of the risks each side carries, and a pre-signing checklist. The aim is a resource a founder, an investor, a tax adviser, and a judge can all follow.