Underlying Asset Performance: The primary driver is the performance of the underlying assets (stocks) held by the ETF. A rise in the value of these holdings directly increases the ETF's NAV and price.

Supply and Demand: Market supply and demand for the ETF shares themselves also affect price. Higher demand tends to drive the price up, while increased selling pressure can push it down.

Investor Sentiment: Overall market sentiment and investor appetite for risk significantly influence demand for ETFs, thus affecting their price.

Tracking Error: The degree to which the ETF's performance deviates from its benchmark index can impact its attractiveness and price. Lower tracking error is usually preferred.

Expense Ratio: The ETF's expense ratio (management fees, operating costs) indirectly affects its price by reducing its overall return relative to the underlying assets.

Liquidity: Higher liquidity, meaning ease of buying and selling, generally makes an ETF more attractive and may contribute to a higher price.

Index Composition Changes: Revisions in the composition of the underlying index tracked by the ETF can lead to price adjustments as the ETF portfolio is rebalanced.