Harberger Tax (COST)
A self-assessed property tax under which owners name their own price and must sell at it — a modern extension of Georgist principles popularized by Radical Markets.
Definition
A Harberger tax, also called a Common Ownership Self-Assessed Tax (COST), requires owners to self-assess the value of an asset, pay a tax on that value, and stand ready to sell at the declared price to any buyer. This neatly solves the assessment problem (owners reveal true values) and the holdout problem (assets are always for sale), while taxing the value of holding the asset.
Relationship to Georgism
COST is a generalisation of the Georgist idea: it captures the holding value of assets — most powerfully land — and discourages unproductive hoarding. Applied to land, it functions like a self-assessed land value tax that also keeps sites liquid. It directly addresses the objection that land can't be assessed.
Origins and Reception
Named after economist Arnold Harberger, the mechanism was popularised by Eric Posner and Glen Weyl in Radical Markets (2018). It has been influential in technology and crypto circles — Ethereum's Vitalik Buterin endorsed it as a tool for property and digital-asset reform.