This is an empirical study of the determinants of stock holdings using data from the US Survey of Consumer Finances from 1992 to 2001. There is a great heterogeneity in the way households form their portfolios. Stock ownership is positively correlated with various measures of wealth, age, retirement savings, and having sought financial advice. It is negatively correlated with holdings of alternative risky investments, such as investments in private businesses, and with the willingness to undertake non-financial investments in the future. While we can predict reasonably well who holds stocks, we have less predictive power about the share of stocks owned by those who hold positive amounts.