Often the yields on TIPS are negative. This is because after taking into account the effects of inflation, the real yield is negative. For instance, if standard 2-year Treasuries yield 1% but inflation is 2%, then the real yield is -1%. TIPS are meant to keep up with inflation, not beat inflation, thus you can have a nominal yield on TIPS that is positive but a real yield that is effectively zero. Note that while the yield on TIPS may be negative, their principal value will increase with inflation, which can generate capital gains.