How do low real interest rates constrain monetary policy? Is the zero lower bound optimal if the real interest rate is sufficiently low? What is the role of forward guidance? A model is constructed that can in- corporate sticky price frictions, collateral constraints, and conventional monetary distortions. The model has neo-Fisherian properties. Forward guidance in a liquidity trap works through the promise of higher future inflation, generated by a higher future nominal interest rate. With very tight collateral constraints, the real interest rate can be very low, but the zero lower bound need not be optimal.