This thesis revolves around banking behavior and its implications for financial stability. The first chapter examines how banks buy and sell securities during the crisis, and we find that some banks -the ones specialized in trading and better capitalized- increase their exposure to securities during the crisis, in particular for securities that fell in price, but reduce lending. The second chapter identifies the lending channel of reserve requirements by studying a change in the policy in Uruguay. We find that reserve requirements decrease credit supply after the policy shock, although this reduction is less important for riskier borrowers, and it is binding for firms. The last chapter reviews the methods to estimate competition in...