In linear colliders preservation of the phase space density of charged particles during acceleration to high energies is essential. In practice, the electromagnetic fields which govern the beam transport may not be sufficiently well understood. This may arise, for example, from magnet and structure alignment and/or manufacturing errors, time-varying electromagnetic fields due to component vibration or imperfect regulation, or at high beam currents, from beam-induced fields. These inadequacies may be overcome using measurements of the beam response. In this report we review such methods for preserving single-bunch beam emittances with experimental results from the Stanford Linear Collider. ©2001 American Institute of Physics.