Adverse possession is the common-law rule by which a trespasser who occupies another's land openly, continuously, and without permission for a statutorily fixed period - commonly ten or twenty years - acquires title, extinguishing the rights of the former owner. That the law should reward a wrongdoer at a rightful proprietor's expense has struck many as paradoxical, and the doctrine's endurance has provoked a long contest among competing justifications, no one of which accounts for all of its contours. The oldest rationale is punitive. The dispossessed owner, on this view, has slept on his rights; by failing to eject the intruder within the limitations period he forfeits his claim as a penalty for inattention. The account draws support from the doctrine's indifference to the possessor's state of mind: because the wrong to be corrected is the owner's neglect, it is unsurprising that whether the possessor knew he was trespassing or believed the land his own makes no difference. Yet the punitive theory sits awkwardly with the uniformity of the limitations period. If the doctrine existed to penalize neglect, one might expect the penalty to track its gravity; instead the owner absent for a generation and the owner a single week tardy in suing are treated exactly alike, and the possessor one day short of the period takes nothing however careless the owner has been. A second rationale looks not to the owner's fault but to the possessor's reliance. Over years of undisturbed occupation the possessor builds, plants, and orders his affairs around the assumption that the land is his; to eject him after decades would upset settled arrangements and destroy the investment his reliance has produced. This theory explains why possession must be continuous, and why a brief interruption resets the clock. But it strains to justify awarding title to a possessor who has made no improvements whatever - a bare occupier the doctrine rewards as readily as the diligent cultivator. A third rationale is administrative. Titles grow stale: witnesses die, deeds are lost, and beyond some point the cost of adjudicating ancient claims outruns any benefit. By quieting title in the long-standing possessor the doctrine spares courts the reconstruction of a distant past and lets present arrangements stand. Like the punitive account, this rationale is indifferent to the possessor's state of mind, matching the doctrine's operation; but it proves too little, for it cannot justify extinguishing an owner's claim even where the records are pristine and the facts undisputed, as the doctrine nonetheless does. The endurance of adverse possession may lie less in any single justification than in the convergence of several. Each theory captures some fraction of the doctrine's shape; each is embarrassed by a feature the others explain. A rule that no lone rationale can vindicate may still be defensible if the rationales together cover the ground each alone leaves exposed. What such an eclectic defense forfeits is the tidy derivation of doctrine from principle that the rule's critics demand - and, perhaps, any assurance that its boundaries have been drawn where they should be rather than merely inherited.