With its interest rate instrument at the zero lower bound, the Federal Open Market Committee has turned to unconventional methods to stimulate economic growth and increase employment. Prominent among these is quantitative easing (QE) — the purchase of a large quantity of longer-term debt. Policymakers and analysts have argued that QE works through the so-called portfolio balance channel: it reduces long-term yields by reducing the term premium investors require to hold long-dated securities. I present several reasons to be skeptical of the theoretical foundations of this portfolio balance channel and offer several arguments for why the effect of QE might be relatively small even if it is theoretically valid. Consistent with these arguments, an empirical analysis using a variety of interest rate variables and public debt supply measures used in the literature finds essentially no support for the portfolio balance channel.