IPO offers access to the newest publicly traded stocks in an ETF wrapper. Companies that have gone public within the last three years and that meet the index's size, liquidity, and free float criteria are included. The fund removes a firm after three years of public trading. The resulting portfolio complements the overall equity market, as its weighted average market cap will ordinarily be far smaller, and its constituents may not be included in major indexes for a few months. The small number of eligible securities can make for a concentrated portfolio. Index constituents have a 10% issuer cap and are reviewed quarterly. Post-IPO liquidity can be a challenge for market makers looking to create new shares, so keep a sharp eye on trading spreads.