Handjeklap was a hand-clap, open-outcry auction method established in the 17-century Amsterdam Exchange.

Handjeklap was a hand-clap, open-outcry auction method established in the 17-century Amsterdam Exchange. Sellers and buyers alternately slapped the back of each other’s hand while shouting their prices; with every clap the quoted figure moved up or down. A seller began with a high ask, the buyer clapped back with a lower bid, and the price zig-zagged until it converged. When both sides agreed, they sealed the deal with a firm handshake, wrote the contract on the spot, and settled later at the Bank of Amsterdam.

Multiple pairs performed the same ritual simultaneously, so overall prices shifted whenever fresh news—such as a ship’s arrival, the course of a war, or the quality of a spice cargo—hit the floor; morning highs could reverse into afternoon lows. In effect, handjeklap functioned as a human-powered continuous double auction: by gathering people and information around one pillar, it created liquidity and allowed demand and supply to rebalance in real time.

Prices not only wobbled clap by clap but also swung throughout the day, serving as a price-discovery engine no different in principle from today’s electronic order book that matches bids and offers in microseconds. Volatility soon posed problems: in 1609 a bear raid via short selling triggered a sharp drop, prompting authorities to outlaw sales without prior ownership—the world’s first short-sale ban. Professional traders emerged, exploiting arbitrage between Amsterdam and regional markets and using forward contracts to pocket spreads, all negotiated under the hand-clap ritual.

Thus, the dynamics we now associate with modern stock pricing—negotiated price setting, intraday swings, regulation to curb excesses, and arbitrage by specialists—were already fully formed on the Amsterdam floor, proving that the psychological and institutional DNA of today’s markets was present four centuries ago.