  Observations of high-redshift Type Ia supernovae (SNe Ia) have provided
strong evidence that the dark energy is real, and making further accurate
observations of high-redshift SNe Ia is the most promising way to probe the
nature of the dark energy. We discuss one of the concerns about such a project
- that of coping with SN Ia evolution. We emphasize that SN Ia evolution
differs in an important respect from the kind of evolution that has foiled some
past projects in observational cosmology, and we outline empirical strategies
that will take it into account. The supporting role of physical models of SNe
Ia also is discussed. Our conclusion is that systematic errors due to SN Ia
evolution will be small.
